Unit of Fire

[kgbudge]

That's exactly right, Mike. The Germans believed common doctrine was necessary for Auftragstaktik to be successful.

[jwsleser]

A brief step back to unit of fire. I just read this thread and let me clarify this a bit, although KgBudge has the basic idea.

Basic load is a post WWII term for a unit level Prescribed Load and reflects the authorized ‘organic’ ammunition for a specified unit, normally battalion size. Prescribed Load (WWII term) only addresses individual systems/weapons (the BAR gunner will carry X rounds), and is not generally totaled up as a unit basic load. It is less than a unit of fire.

Unit of fire is (WWII) the expected daily consumption of ammunition by type weapon in combat.

Day of supply is a campaign planning figure for consumption of ammunition over extended periods of time and is an aggregate of the theater for long-range projections. For example, I am planning Sicily. I expect the fighting to last 60 days. There are 100 30 cal heavy machineguns in the entire force (including those carried by messhalls, shoe repair units, etc.). So 100 (number of total weapons) x 150 (rounds per day) x 60 days = 900,000 30 cal heavy machine gun rounds required for the 60-day campaign. 900,000 rounds /100 MGs = 9000 round per weapon. Unit of fire is 3000 rounds, so my invasion force needs three units of fire for the campaign for the 30 cal Heavy MG.

When you read the Panzer Army in NA had only 3 units of fire on hand, it means that if every weapon of that type was in combat, they could fight for three days. Of course, the ammunition for the shoe repair unit can be given to the infantry battalion, as the shoe repair unit will only fight for a few minutes. This automatically builds in a reserve/safety feature for adequate stocks. If you are a corps planner, you don’t need to guess are the time and duration of combat if your planning numbers are decent. If you are UK XXX corps planning 3rd Alamein, you plan 6 days, at the day of supply rate for all your weapons (TO&E numbers), divided by unit of fire to request your ammo stockage/planned consumption. This system works better for long times and larger forces. If you knowe how many days you will be in combat (an artillery battalion and you plan to fire for 6 days straight during Alamein), then 6 units of fire are required.

While I didn't serve in WWII, I did stay at a Holiday Inn. (plus serveral years as an army level planner, bde log officer executing several deployments, etc.) I do keep my copy of FM 101-10-1/2 handy in my office.

Jeff

[kgbudge]

Jeff, thanks for confirming and extending my basic understanding. I think I have my brain wrapped around the concepts reasonably well now.

[Carl Schwamberger]

It seems so simple as Jeff explains it. Think I'll memorize that text for the test.

[takata_1940]

I was wondering if those with some knowledge of the subject could take a look at this table and help me understand: http://pwencycl.kgbudge.com/U/n/Unit_Of_Fire.htm

Hi,
I'm going to contradict almost everybody in this thread... only RichTO90 cited the manual.

1. Unit of fire (UF) is a space/load unit computed arbitrary and it is not related to any "daily expenditure". The daily expenditure showed by this table was computed at very high echelon (Army, Army Group/Theater) during long period of time. It would be very different at Platoon's level during one single week of combat. Then, it is not possible to make absolute statistics on it. This will make sense only at the highest logistical level.

2. This table is certainly confusing the dotation carried per weapon (excluding higher echelons ammo) and UFs. UFs are usually expressed in much higher numbers: i.e. 575,625 rounds of 30. Rifle (with packaging), which will fill a 10 metric tons wagon (or whatever space). It is computed for each caliber and it will be used on purpose of replenishment computations.

3. US "unit of fire" were settled before the war on the basis of WWI experience and derivated for new weapons. Actual WWII consumptions were vastly different and varied also from one theater to another. Then, real consumption of UF would be monitored by HQs and new tables for planning revised accordingly, saying that x-sized unit will need y-UF of z-ammo per day/week/month. Then, this base would be multiplied by another factor considering the consumption rate due to different combat posture forecasted during planning (exploitation, heavy fighting, etc.).

S~
Olivier

[Carl Schwamberger]

I was wondering if those with some knowledge of the subject could take a look at this table and help me understand: http://pwencycl.kgbudge.com/U/n/Unit_Of_Fire.htm

Hi,
I'm going to contradict almost everybody in this thread... only RichTO90 cited the manual.

1. Unit of fire (UF) is a space/load unit computed arbitrary and it is not related to any "daily expenditure". The daily expenditure showed by this table was computed at very high echelon (Army, Army Group/Theater) during long period of time. It would be very different at Platoon's level during one single week of combat. Then, it is not possible to make absolute statistics on it. This will make sense only at the highest logistical level.

2. This table is certainly confusing the dotation carried per weapon (excluding higher echelons ammo) and UFs. UFs are usually expressed in much higher numbers: i.e. 575,625 rounds of 30. Rifle (with packaging), which will fill a 10 metric tons wagon (or whatever space). It is computed for each caliber and it will be used on purpose of replenishment computations.

3. US "unit of fire" were settled before the war on the basis of WWI experience and derivated for new weapons. Actual WWII consumptions were vastly different and varied also from one theater to another. Then, real consumption of UF would be monitored by HQs and new tables for planning revised accordingly, saying that x-sized unit will need y-UF of z-ammo per day/week/month. Then, this base would be multiplied by another factor considering the consumption rate due to different combat posture forecasted during planning (exploitation, heavy fighting, etc.).

S~
Olivier

Is this not covered by the paragraphs from the FM 6-9 I posted on 20 March?

I've been back into that doc. twice in the past week and found it facinating. Wish there was time to read the entire text throughly. It has the apperance of being written by people who suceeded or failed in fairly concrete terms. Which makes me wonder who wrote that particular edition. The US Army had little opportunity to test any of this post 1918, being hard pressed to conduct any exercises larger than a brigade or occasional division.

[jwsleser]

Oliver

Not a problem with you questioning what I posted. Of course, I certainly disagree with your understanding of the workings of ammunition supply. Let me provide a detailed discussion using the period manuals.

The purpose of unit of fire (UF) and Day of Supply (DS) is to make the process of requesting and receiving ammunition as simple as possible. The unit of request can be based on shipping (a pallet of ammunition/a standard weight) or consumption. A quick look at the tables in FM 101-10 (15 June 1941) shows that standardized shipping wasn’t the common factor used. Additionally, UF and DS are established by theater, not by a central transportation/shipping authorized (FM 9-6 para 11 and FM 101-10 para 107). It is hard to find a useful purpose in a “standard space/load computed arbitrarily” value if no one is using the same value.

I will introduce a new term, credit.

A credit is a definite quantity of supply placed at the disposal of the commander of an organization for a prescribed period of time... In establishing credits for ammunition, the numbers of rounds by caliber and type are prescribed as available for a definite period of time. In theaters of operation where a unit of fire has been adopted that establishes a definite number of rounds per weapon by type of ammunition, the unit of fire is used to express the amount of credit allocated.(FM 101-10 para 107, and also mentioned in FM 9-6).

A credit can be either a UF or a DS, and is designated by the theater. So here we have a unit of time associated with a quantity of ammunition and both UF and DS must have a quantity and a time.

Ammunition, like all classes of supply was requested and provided daily. This is because the human biological cycle, nights and days, and exhaustion generally create lulls every 24 hours. Resupply is essentially a daily (24 hour) cycle. So a unit needs to possess enough ammunition to last through a 24 hour period before it needs to be resupplied. First……

Depots and ASP's. There are two main types of ammunition supply installations, namely, depots and ASP's (ammunition supply points). Either may be defined as an organized locality for receiving, classifying, storing and issuing ammunition. The distinction between them is that the bulk of ammunition handled by ASP's is issued directly to combat units, while most of the ammunition issued by depots is to other ammunition supply installations. (FM 9-6 para 50.a.).

So ASPs issue ammunition directly to combat units. Now….

Each ASP must have a sufficient quantity of each type of ammunition to insure that the troops it supplies can replace each day's expenditure before beginning the following day's operation. (FM 9-6 para 54).

This reinforces the 24 hour cycle I mentioned above. Now logic.

If you are only planning to resupply once a day (24 hours), the resupply must be in enough quantity to last another day. Combat is cyclic; there are good days and bad days. You will never fully predict what each day will require. In this case, the unit of fire is a daily average that can account for most situations. If you look at the table in para 93 in FM 101-10 (AMMUNITION REQUIREMENTS PER DAY OF COMBAT EXPRESSED IN UNITS OF FIRE), of the 62 possible values in that table, 39 are one UF. So greater than half the situational daily ammunition requirement is met by a UF.

Now when you compare this relationship to the number of rounds in a unit of fire for like weapons, the quantity/duration (consumption) relationship becomes more prominent. In para 92 of the same manual, the 75mm gun has two types of rounds, HE (assumed) and AT. The HE and AT have the same weight, yet the UF of the HE (300) is twice that of the A.T (150). To any artilleryman, this makes perfect sense when talking consumption and not shipping.

So UF traditionally is a day of consumption. Because nothing is certain in war, manuals allow one to modify if there is sufficient reason to do so. This is why a period of time or quantity is not specified, but left to the commander. To say an army has 3 UF available means nothing to a planner if it reflects transport, especially as the UF have different transportation requirements. But if UF means consumption, 3 UF has a lot of meaning to a commander and planner, regardless of the type of weapon. A report on theater stockage expressed in UF (2 UF artillery, 4 UF of small arms, 1 UF of AT) carries a lot of meaning and understanding of the current status of one’s force to a commander when it reflects consumption over time.

To recap using the manuals. A time is associated with a UF, which makes a UF a rate of consumption, not a unit of transport. While the time over which the ammunition is consumption is a dependent variable, it is dependent by theater (or lower if the command wishes it), not a by a central transportation command. A DS is use to calculate consumption over time when the nature of operations is unknown or of a very long duration (for planning). A UF provides consumption when the nature of the operations is know and generally addresses a short period of time. Generally, theater plans using DS, while subordinates plan using UF.

Finally UF were settled before WWII only until WWII started. The planning data used in this and other planning factors are constantly updated as new data is generated. Consumption over time in conventional war doesn’t change much as weapon systems didn’t change much. UF likely didn’t change much, while DS changed a lot.

Please feel free to question and ask. I back this up with a lot of experience. And we haven’t yet touched on Required Supply Rate (RSR) and Controlled Supply Rate (CSR). These are modern terms, but address the additional use of the DS within theater during WWII.

Pista!

Jeff

[takata_1940]

Hi Jeff,

Not a problem with you questioning what I posted. Of course, I certainly disagree with your understanding of the workings of ammunition supply. Let me provide a detailed discussion using the period manuals.

I made it short and I certainly could have expressed it better, but be sure that my understanding of ammunition supply is fine.

The purpose of unit of fire (UF) and Day of Supply (DS) is to make the process of requesting and receiving ammunition as simple as possible. The unit of request can be based on shipping (a pallet of ammunition/a standard weight) or consumption.

You are introducing a confusion making both terms "Unit of Fire" (UF) and "Day of Supply" (DS) barely interchangeable. I can prove they are describing something different, hence the existence of two terms whith different meanings. As of their purpose of making it easier for requesting and receiving ammunitions, this is not the case as the easiest way for the end-user is to request x-number of y-caliber rounds without using any conversion table. Their purpose is for planning ammunition flows at the highest echelons - much higher than end-user's level (troops) which are placing basic orders for ammunition replenishment.

A quick look at the tables in FM 101-10 (15 June 1941) shows that standardized shipping wasn’t the common factor used. Additionally, UF and DS are established by theater, not by a central transportation/shipping authorized (FM 9-6 para 11 and FM 101-10 para 107). It is hard to find a useful purpose in a “standard space/load computed arbitrarily” value if no one is using the same value.

Maybe I was not clear enough. I didn't said it was based on "standardized shipping" (like palets and containers) but on weight/space values computed arbitrarily, or more exactly, computed empirically. It is always derived from any previous battle experience or theoretical assesments. Consequently, it may be wrong if conditions of the fight had drastically changed from initial computation or if assements were wrong. That's why theater's HQ may need to use different UFs. Nonetheless, the real ammunitions are still shipped in "standardized loads" usally using standardized vehicles, trains and ships, before being broken down into sub-loads down to the end-user. Some of such standardized loads are planned as to contain several UFs of x-caliber and/or a mixed UF content of different calibers. This is the case for standard ammunitions trains and ships supplying the same theater of operation where the same "Units of Fire" value is in use.

Then, why "Unit of Fire" is different from "Day of Supply"?
- the basic answer is that how long a "Unit of Fire" will last is an unknown factor. It is easy to show that it may last forever or that it may be fired in few minutes at each weapon's sustained rate of fire. consequently, it cannot be the basic computation factor for planning ammo requirements that are just too erratic and may vary from zero to nearly an infinite number. On the other hand, the "Day of supply" unit is used for computing supplies that are expended on a regular basis, like food, drinkable water, animal's forage, etc. Moreover, if high level statistics may reveal some "daily figures" for ammo consumption, one should keep in mind that those figures are not reflecting the real requirements for ammo (or specific ammo) but, in reality, their availability for the end-user considering the supply chain overall efficiency or the stocks at disposal.

What is then the purpose of using "Units of Fire" tables?
- For planning, one need to translate the requirements of all different ammunitions into one single unit for moving it from the factories to the battle-zone, but also inside each level of combat units and, above all, their repartition. The serious constraints for moving ammo are weight and/or space. As each combat unit is using different weapons with different ammunitions, one will need to know the ratio of those ammunition's weight/space taken in order to divide the total load/space available that will be assigned for each caliber loads. The unit used is the "Unit of Fire" which represent, in theory, the balanced unit's rate of consumption of all calibers (compared to each others).

Example 1: I want to load one 10,000 DWT cargo ship with ammo for my Infantry division. I will assign to each caliber used in the Infantry division a fraction of the whole cargo capacity. This fraction should be computed on the basis of 1 UFs per caliber. Hence, my supply should be balanced. A look at my table is showing that the "Infantry division UF" (the summ of all caliber UFs) is, say 500 tons. I can load then 20 divisional UF. Next, I multiply each caliber UF number by 20 in order to find out how many "standardized packages" I will order from the depot.

Example 2: I need 20 UF for my division and I would like to know how many ships are necessary to carry it: here 10,000 DWT but I can only find one of 6,000 dWt and another one of 4,000 dwt ; I'll load 12 UF of my division's ammo (meaning 12 of each caliber) into the first ship and 8 into the second. Hence, even if one ship is lost, I'm still able to supply all the weapons of my unit at the (theoretical) same rate during a certain amount of time.

I will introduce a new term, credit.
A credit is a definite quantity of supply placed at the disposal of the commander of an organization for a prescribed period of time... In establishing credits for ammunition, the numbers of rounds by caliber and type are prescribed as available for a definite period of time. In theaters of operation where a unit of fire has been adopted that establishes a definite number of rounds per weapon by type of ammunition, the unit of fire is used to express the amount of credit allocated.(FM 101-10 para 107, and also mentioned in FM 9-6).

Nothing about "credit" will contradict what a UF is, namely a ratio showing the planned rate of various ammo consumption by a combat unit during a "definite period of time" (usually a long one as this is not the case for low level units and for short periods of time).

A credit can be either a UF or a DS, and is designated by the theater. So here we have a unit of time associated with a quantity of ammunition and both UF and DS must have a quantity and a time.

As I explained above, the unit of time is known for DS, "daily"... but is an unknown factor concerning UFs: it will last "a certain time" depending on intensity of fight which is beyond planning as the enemy may seriously alter planning.

I'll snip the rest which doesn't clarify anything

So UF traditionally is a day of consumption. Because nothing is certain in war, manuals allow one to modify if there is sufficient reason to do so. This is why a period of time or quantity is not specified, but left to the commander.

This is a serious misunderstanding of the whole concept. One Theater commander may realize that his supply of AA ammo is always short when his stockpile of small arms ammo is growing after each new delivery of ammos (when pre-planned shipments are used). This would mean that the shipping space is not optimal and doesn't reflect the ratio of expenditures and combat needs. Then, there is two options: to modify the the number of AA UFs (up) and small arms UFs (down) per shipment. Or to change the amount of rounds per AA UF or small arms UF inside his theater. Usually, the fist method is more commonly used:

FM 9-6 citation:

(14) Unit of fire. A unit of measure for ammunition
supply within a theater from a tactical point of view, based
upon experience in the theater. It represents a specified
number of rounds per weapon, which varies with the types
and calibers of the weapons. The unit of fire is not synonymous
with the term "day of supply" (see (7) above). In
general, it represents a balanced expenditure by the various
weapons under conditions of normal action. The unit of fire
prescribed by the War Department may be modified by
theater commanders as necessary for each individual theater.

(7) Day of supply. Estimated average expenditure of
various items of supply per day in campaign, expressed in
quantities of specific items or in pounds per man per day.
A day of supply for ammunition is expressed in rounds per
weapon per day.

In the case of allocation of "Day of Supply" for ammunitions, the allocation would have to last until the next day, which doesn't mean it will be fine depending on the tactical situation.

As a conclusion, the UF concept is based on the same factor as the prescribed loads at various echelons. If an Infantry soldier is recieving a 150 rifle ammo load and a mortar team 60 rounds, this doesn't reflect an absolute need (daily expenditure or whatever), but their capacity to carry it without losing too much mobility, or making a too long vehicle column, etc. On the other hand, it is expected that both load are balanced to be expended during the same undetermined period of time.

S~
Olivier

[jwsleser]

Oliver

Interesting discussion.

I need to clarify where our disagreement lies. My understanding of your position is that the number of rounds in a UF was selected/established based on shipping requirements (cube/weight), not consumption over time. If my understanding is incorrect, please tell me what the number of rounds in a UF is based on?

More to follow if needed.

Pista!

Jeff

[Cannonade]

Have perused the posts on this thread, and wish to commend everyone for contributing informed, thoughtful posts on the subjects under discussion.

One small point remains to be made.

Following the successful lodgement in Normandy, the shortages of artillery ammunition led to rationing. This rationing was expressed in Day of Supply expenditures for each of the armies. In December 1944, shortages reached the point that SHAEF had to order theater wide rationing which was also expressed in Day of Supply. Expenditures at the army level were recorded in Day of Supply, which directly impacted the bids made for allocations of resupply from COMZ via ADSEC and CONAD. Fire plans were written in terms of Day of Supply, and relied on existing stocks in the ASPs plus guaranteed (promised) deliveries. As a result, armies were faced with having to save (hoard) artillery ammunition in order to have sufficient stocks on hand to provide the Day of Supply required to support planned operations. For example, the SHAFE Day of Supply for 105mm Howitzer ammunition of the most common types was around 25rds/gun/day (I may be off a little here, as I am working from memory.), but with careful savings through tightly controlling expenditures where ever possible, stocks were raised sufficiently to authorized Fire Plans utilizing a Day of Supply of over 100rds/gun/day for the same ammunition. Conversely, strict rationing in terms of Day of Supply led to artillery units firing their allocation, and then telling the units they were supporting that they could fire no more that day. Vicious circle.

Cannonade

[jwsleser]

Cannonade

Very true. This is what I was alluding to with my comment about Required Supply Rate (RSR) and Controlled Supply Rate (CSR). The Day of Supply (DS) can be used to control/ration expenditures. These are both tools to mange ammunition.

The DS, if reflecting historical consumption, can be used to plan for further expenditures. This is when it is used by higher headquarters for planning. However, the DS can be used to limit consumption for subordinate units. This now becomes a credit per FM 101-10. Units can only draw the DS for expenditure. Today, the DS is no longer used, but has been broken down into RSR and CSR. I calculate my future ammunition requirement using the RSR, but I control expenditure using the CSR (if my CSR from higher is less than my RSR).

Jeff

[takata_1940]

Hi Jeff,

I need to clarify where our disagreement lies. My understanding of your position is that the number of rounds in a UF was selected/established based on shipping requirements (cube/weight), not consumption over time. If my understanding is incorrect, please tell me what the number of rounds in a UF is based on?

It was established arbitrarily: why say 150 rounds per gun and why not 300 or 500?
The major constraint is mobility taking into account the space and men available for moving such ammo, or the space available for moving units or to replenish them. Hence, it is reflecting the various TOEs dotations in arms, men and vehicles, the supply chain organization, and this UF overall weight ratio empirically based on balanced consumption.

Where it is confusing is that during large periods of time, at Army or above level, it will show that it is close to statistical daily expenditures but this is like eggs and chicken stuff. Are those statistics reflecting the consumer needs or the availability of ammo for the end-user?

If your whole system is organized around a daily replenishment of such numbers (as it is), it cannot translate in twice or more this consumption rate. On the other hand, the variations during the period considered are in the range of factor 10 or more, then are reflecting the need for making stockpiles in order to face peak consumption periods.

S~
Olivier

[jwsleser]

Oliver

There are many bits in these manuals, but arbitrary data is not one of them. The process, procedures, and data (values) are all based on historical information, experience, and a methodology. The information present, while not 100% reliable (after all, we are discussing war), is good enough for planning until detail data for specific event can be developed.

Oliver: It was established arbitrarily: why say 150 rounds per gun and why not 300 or 500?

It was established based on historical data, modified by anticipated changes due to doctrine and weapons. This is why a rifle (M1903) has a UF of 150 rounds, a semi-auto rifle (M1) has a UF of 750 rounds, and a LMG (BAR) has a UF of 2,000 rounds (FM 101-10 para 90.b). This is not WWI data alone (the US didn’t have a semi-automatic rifle in 1918), but WWI data modified by anticipated changes created by new doctrine and weapons. These values have internal logic when you think of a bolt action rifle, a semi-automatic rifle, and a machine gun firing over a period of time.

In the case of a Unit of Fire (UF), the original source that started this discussion

http://pwencycl.kgbudge.com/U/n/Unit_Of_Fire.htm

states “The unit of fire roughly corresponded to the amount of ammunition consumed in one day of combat.”

FM 9-6 para 5.a.14 states of a UF….”In general, it represents a balanced EXPENDITURE by the various weapons under conditions of normal action.” (my Caps). The UF express consumption of ammunition, not transportation or some arbitrary value.

The table in 101-10 para 93 in FM 101-10 is titled “Ammunition REQUIREMENTS per Day of Combat expressed in Units of Fire” (my Caps). Again, a requirement based on consumption in which a UF more often than not reflects a 24 period of expenditure.

If you study the table at para 93, the UF is designed, more often than not, to meet the daily EXPECTED usage when in combat. There are situations that will require more, and some that will require less. It is a forecast for planning so the logistic toads can move and stock the required the required supplies in preparation for the planned event.

If you can’t understand this point, it is fruitless for me to continue this discussion. I have reread your comments several times and you don’t describe a system that can forecast and program ammunition supply. All you have shown is the ability to calculate shipping space once a requirement is determined. Since the purpose of the UF and DS is to create the REQUIREMENT so someone can calculate shipping space, you have completely missed the rational of the values embedded within the UF and DS.

I am more than happy to continue this discussion using the understanding of the planning factors I have presented. If you still disagree, that is okay. I will quietly drop-out of this discussion.

Have a great day!

Pista!

Jeff

[Schpam]

Jeff,

One quick correction the UF table says 150 rounds for .30 rifle and 750 rounds for .30 BAR. Rifle could mean M1903 (bolt action)and/or M1 Rifle aka M1 Garand (semi-auto). BAR should be self-explanatory. I believe the reason the .30 rifle, .30 BAR< and .30 MGs are all totalled together is that they all used the same .30 ammuntion.

V/R
Paul

[jwsleser]

Paul

Good catch. Thanks for checking. I had to check and found the proper nomenclature for the BAR is Auto-rifle, M1918. I assumed the LMG was the BAR. My error. But it still makes my point. If you are using an arbitrary numbers for calculations, why give four weapons that use the same ammunition four different UFs? Instead of simplifying the calculations, you have created another layer of complexity by adding another arbitrary variable.

Pista!

Jeff