1940 'Emergency Batteries' Question.

[Paul_G_Baker]

Folkestone East Battery - No. 1 Gun Emplacement (Repurposed and redecorated!).


Folkestone East Battery - No. 2 Gun Emplacement.

The photos, above, seem to be fairly repesentative of 'Emergency Battery' emplacements. Looks like a lot of digging and concreting was required before guns could be installed and brought into action.

Add to that the time necessary for the concrete to 'cure' (i.e. harden and develop its strength) sufficiently. Wikipedia (for what that's worth) indicates around 90% strength after 4 weeks.

Also add the construction time for the Battery Observation Post, Searchlight Emplacements/Control Positions and tunnels or covered trenches for both moving aboout safely and sheltering from enemy fire.

The question is, how long did those Emergency Batteries each take to build?

[Knouterer]

The short answer would be: a few weeks. It would depend on, among other things, the accessibility of the site, local availability of materials, etc. It seems that in general the guns were installed first and made ready to fire, and subsequently gun houses were built over them. I vaguely remember a reference to quick-setting concrete.

Setting up the BOP, magazines, searchlights etc. could take a little longer. Some batteries were reported as ready for action "by day only" initially.

Improving the local defences with wire barriers, mine fields etc. was an ongoing process, in 1941-1942 Bofors guns, Spigot mortars, 75 mm field guns etc. were added. In 1940 local defence was usually limited to one or two Lewis MGs.

See for a practical example this thread about the battery at Seaford (343 Battery): http://sussexhistoryforum.co.uk/index.php?topic=6073.0

Drawing is from "20th Century Defences in Britain - An Introductory Guide" (ed. Bernard Lowry).

[Paul_G_Baker]

Some info on quick setting concrete here:- http://www.rdso.indianrailways.gov.in/u ... page_3.pdf

The elevation drawing of the emplacement looks exactly like the No. 2 Emplacement at Folkestone East - apparently only the No. 1 Emplacement ever had an attached ammunition store (as per the diagram), though.

[Carl Schwamberger]

Add to that the time necessary for the concrete to 'cure' (i.e. harden and develop its strength) sufficiently. Wikipedia (for what that's worth) indicates around 90% strength after 4 weeks.

That would be accurate. I used to be in the materials testing business. The standard US concrete of the 1970s we tested went over 50% in one week & better than 90% at the 28 day test. That was strictly a compression test & might not directly relate to resistance to projectile impacts or explosive detonations.

[Paul_G_Baker]

Thanks for confirming, Carl.

[Knouterer]

According to J. Goodwin, Defending Sussex Beaches 1940-1942, p. 63, the concrete roof of the gun houses was 9 inches or 23 cm thick. That would have provided reasonable protection against German 50kg bombs.

According to this interesting list from W. Fleischer, Deutsche Abwurfmunition bis 1945, against concrete up to 20 cm thick the recommended projectile was the standard 50kg HE bomb (SC-50), provided it was Quality Class I (with a stronger bomb casing than Class II and III and less likely to break up on impact) and that it was dropped from a height of at least 1,000 m. For concrete up to 50 cm, 250kg bombs are recommended. For some reason, there was a large gap in the German arsenal between bombs of the 50kg and 250kg class.

[Knouterer]

Upon reflection: that is too optimistic. The US Army Corps of Engineers published various manuals during the war about the effects of bombs and shells, thicknesses of various materials required to resist various calibres, &c.

According to TM 9-1907 (of 1944) a 100lb (45kg) general purpose bomb (AN-M30 or AN-M30A1), if dropped from an altitude above 5,000 ft, would probably perforate 1 foot of 3,400 p.s.i concrete and 0.75 ft of 5,000 p.s.i. concrete.

However, even if a bomb did not perforate, i.e. go all the way through, it might cause scabbing, i.e. concrete fragments would break off on the underside of the concrete slab. According to TM 5-310 (also from 1944), "Tests indicate that scabbing occurs in concrete when the penetration of a bomb becomes greater than about 50% of the slab struck."

Assuming the bomb to be delay-fuzed, as would normally be the case, the explosion would then increase the penetration, but not by very much compared to impact penetration.

Nevertheless, still according to the same series of manuals, for adequate protection against such 100lb GP bombs 3.5 feet of reinforced concrete would be required, which is of course a lot more than nine inches which (allegedly) was the thickness of the roof of the gun houses.

[Knouterer]

Interesting picture of gunners in an Emergency Battery training while construction is going on around them, July 1940 (IWM H2459):

[sitalkes]

Also note that the bunkers were partially built of bricks, and though they do have concrete roofs, the front was basically protected only by the gun shield

[Knouterer]

A couple of interesting pictures from the IWM, sadly without date or location, showing gunners in a (from the looks of it) freshly built Emergency Battery, bringing up shells and defending the rear of the battery.

Incidentally, it shows that the Royal Artillery was among the recipients of the American .30 M1917 rifles - distinguishable from the .303 P14 rifles by the longer groove in the stock.

[Knouterer]

For a better view:
http://www.iwm.org.uk/collections/item/object/205378517
http://www.iwm.org.uk/collections/item/object/205378516