Just for curiosity, how many men and aircraft were there by December 10th or 15th?
I've never seen a precise figure for what arrived in the first week, apart from the anecdotal "1,000 more troops" and the P-40s brought in from the U.S. Usually the build-up in the Canal Zone is reported at various "mileposts" - end of calendar or fiscal years, change in Departmental commander, changes in command structure, etc.
But just for curiosity, how passable is that central mountain range to infantry and vehicles?
Here's a MODERN map, showing major metalled roads. Note that
even today there are no major routes THROUGH the central mountains; instead just a series of roads going up ribbon valleys to highland towns like Santa Fe, El Cope, El Valle etc. Any other roads in the mountains are at best going to be down at the "unmetalled" level in the period under discussion -
and that's possibly the most charitable that can be said about them I severely doubt if there were any that were passable for armour or wheeled traffic in the November/December period -
given the rainy season.
http://www.schooneralliance.com/Panama%20map.jpg
Inflitration was not going to work because the locals would be hostile and the units would know next to nothing of the terrain they would be operating in.
This STILL applies to a motorised expedition in the rainy season. The locals don't
actually have to do anything more hostile than lift a telepohone; but as it was, it would be remarkably easy to block trails out of season.
The Canal was not vulnerable to attack, period. But to be systematic about it, all possibilities should be examined and debunked.
Okay ; then bear in mind when modelling this that U.S. garrison has thirty years of experience and training at deployment to resist invasion, by its various levels of transport at various times. By the outbreak of war, with the two para battalions as well as thousands of ground troops and mechanised recce forces as well as mobile tracked artillery (this may be a generous description for the half-track mounted 75's but they still moved and fired LOL) I certainly wouldn't see that these wouldn't have been exercising and training appropriately...and are as mobile if not MORE so than a Japanese expedition limited in speed and roads it can use by its armour. Actually, the source Robert mentions at the very start of the WI
elsewhere describes in detail the degree of mechanisation, and the garrison's development of the road network and cross-isthmian highway in this period. If you factor BACK in your already-mentioned unfamiliarity with the terrain and topography on the part of the invaders, then the garrison would literally be able to run rings round them...given that the terrain and the climate reduces the invaders' movement options to a particular number of choke points on the map - like the coastal plain between Penanome and San Carlos/Chame and on to La Chorrera , for example.
The major disadvantages of using an armed column to attack the Canal are very simple and obvious;
1/ once ashore it's incapable of reinforcement, with the USN moving to secure the coastal
after any putative landing...whereas the defenders are able to air-lift in forces direct from the continental U.S. or other Carribean commands if necessary;
2/ Any action by an open attack like that against the Canal actually means GETTING there and STAYING there - against a force several times in size, with artillery and air support;
3/ It's vulnerable to air attack ALL the way from it's landing point to the Canal; remember, the defenders had had their own well-used bombing and ground-strafing range at Rio Hato for
YEARS;
4/ And then there's the
really major stopper that one radio message to Ernie King stops the
Yorktown in its tracks; a loud, obvious, mechanised attack on the Canal
stops the targets-of-opportunity from even approaching the Canal, let alone getting attacked and damaged there -
reducing the attackers' options BACK to trying to damage the Locks or Dam...and ALSO gives the defenders probably
days to get forces into position at the Canal to hold them away from those points...AND as mentioned up the thread the Locks are both as hard to damage AND as easy to repair as slot in replacement gates or divert around using the closed-for-the-duration parallel sets.
In other words - a land force has as
few options for damaging the actual functioning of the Canal as a mechanism as a naval or aerial attack...while loosing ALL elements of suprise AND having almost no fall-back options. It's actually FAR more vulnerable to attack
itself by the defenders - by blocking forces due to the terrain, fixed point defences on the Canal itself, and by air attack.
The defenders don't even need to be supermen; against an overland expedition they have ALL the advantages. Robert's plan for a time seemed to give his aerial attackers some advantages, before it turned out that these were spurious. An
overland motorised expedition with armour however gives away even the last advantage of suprise.