Did the US even have combat-ready, trained and equiped troops in division size in January 1942, in the continental US, available for deployment
Yes. I'd refer you to Stauntons 'Order of Battle for the US Army in WWII for a 620 page outline of the subject. The eighteen National Guard divisions had been mobilized in the autumn of 1940, reequipped, retrained, purged of political appointees, reorganized into the new triangular structure, retrained to the new doctrine again, & in Jan-March 1942 most were about as ready as any unit without combat experience could be. Note how the majority of the divisions and separate battalions or regiments sent overseas in 1942 were former NG units.
2. The 1st & 2d Armored divisions had been formed up in July 1940 & they also had 18 months training by February 1942. Some personnel were withdrawn to help cadre the 6th Armored Div in Feb 1942, but this was not so large as to disrupt training for more than a few weeks.
3. The 5th Inf Div, a Regular Army unit was never drawn on whole sale for cadres for new divisions. It was kept intact for overseas service & sent to Iceland in April 1942 to replace the Navy/Marine garrison.
4. The 1st, 2d, 3rd, 4th, 7th Inf Div were all Regular Army that were kept intact until May & June 1942. The 1st, 3rd, and 9th ID had been along with the 1st & 2d Marine Divisions part of Fleet Amphibious Forces.
5. The 6th, 8th, 9th, & 10th Regular Army Inf Div were considered fully trained & equipped at the end of 1941. They were tapped for large scale cadre transfers at the start of 1942. It took these RA divisions between 2 & 6 months to work back up to combat readiness after a cadre transfer, depending on how fast the new replacements arrived and other circumstances.
6. The 24th & 25th ID were formed out of the old Hawaiian Division & misc NG units October 1941. Since the bulk of the officers 7 NCOs had previous Regular Army, Army Reserve, or NG training these two did not require a full 18 months for work up. The 25th arrived on Guadalcanal 11 months after activation & fought there until the Japanese evacuated in January.
Not counting the two cavalry divisions the US Army had approx 30 trained and equipped divisions February 1942. The Navy had two Marine Divisions. Leaving aside the nine RA Div used for new unit cadres Feb thru July 42 that left the US with 23 divisions. Plus about 35 Separate Infantry Regiments. Two of the NG divisions had problems passing their readiness test of their training, so the count could be 21 on the low side.
Were the need large enough some of the RA ID, could have been left intact for overseas service as the 5th ID was. This would delay the training of new divisions somewhat. There several ways it could have been worked around, but worst case is the 14 or 15 receiving divisions would not be ready until late 1943 vs midyear.
Marshall had a large officer cadre when the War Powers acts initiated mobilization latter 1940. Unfortunately the War Dept was still much divided against itself & subject deeply to the whims of congressional interests. Marshal was unable to overcome all the obstacles to reorganizing and and rationalizing doctrine during 1941. The legislation accompanying the DoW with Japan, Germany, Ialy, gave the CoS briefly the ability to act without impediment and get the reorganization completed in early 1942. Had the CoS the same power in early 1941 the Army ground forces would have been much better prepared come Jan 1942.
The overseas service of ground combat forces in 1942 was:
1 & 2d Armored: August UK; November Op TORCH
1st ID: November Op TORCH
3rd ID: November Op TORCH
9th ID: November Op TORCH
5th ID: April Iceland
25th ID: Nov/Dec Guadalcanal
27th ID: Feb/March Hawaii
29th ID: Sept/Oct UK
32d ID: April Australia; September combat New Guinea
34th ID: Jan N Ireland; November Op TORCH
37th ID: May Fiji
40th ID: Sept Hawaii
43d ID: Oct 42 Hawaii
1st Marine Div April/May Fiji
2d Mar Div May Samoa
Separate Inf Regiments
3rd: Jan 41 to Newfoundland (Yes I cross checked the date)
4th: Jan 41 Alaska
24th: May 42 New Hebrides
33d: Dec 41 Trinidad
37th: July 41 Alaska
53d: June 42 Alaska
58th: June 42 Alaska
89th: Scattered across Caribbean 41-42
102d: Jan 42 Bora Bora
118th: Aug 42 Iceland
132d: Feb 42 Australia; May New Caledonia; Dec Guadalcanal Americal Div
138th: May 42 Alaska
147th: May 42 Fiji; Nov Guadalcanal Americal Div
150th: Panama
153d: Alaska
156th: Oct 42 UK
164th: Mar 42 New Caledonia
182d: Mar 42 Australia; Dec Guadalcanal Americal Div
201st: Sept 41 Alaska
295th: Puerto Rico
296th: Antilles, Panama, Puerto Rico...
297th: Alaska
298th: Hawaii
367th: April Liberia
434th: Caribbean
503 Parachute: Oct 42 Australia
509th Para: Nov 42 UK; Op TORCH
Point here is in the Separate Regiments & independent support battalions the US Army had the equivalent of another division or two available Jan 42.
The chaos of Allied cargo shipping in 1942 had more to do with the strategic or operational constraints. The rapid escalation of events & the the Pacific 1941 left cargo ship allocation planning useless, and wrong footed for much of 1942. Then there are things like the eight separate regiments in Alaska. Add in all the affiliated artillery, engineer, & support units & there a Arctic corps of three divisions equivalent sucking up cargo shipping for 1942. One can find all sorts of missteps like that as Allied planning adjusted to the new circumstances.
Amphibious Forces Atlantic Fleet were conducting corps size exercises by Jan 1942, so there was that minimal expeditionary capability.