Hi Dwayne, welcome to the forum. We`ll sure try to help you solve your research puzzle. It may take awhile so stick with us, you have a lot of good clues and there will tons of sources & records to check.A couple of things i would suggest is go to a local Library & search newspapers of the time frame, newspapers usualy had some mention of the local boys in WWII.
Another is to contact the local VA Hospital, they may have a copy of his records.
I dont have much time to do a lot of research at the moment, but i found a few things that will help.
The 434th AAF Base Unit was located in Santa Rosa, California, & i think Hamilton Field was close to there.
I wondered why a 23 yr old would be sent back to the States in Dec of `44 unless he was a casualty, but in a Nov `44 report of the 818th EAB there appears to have been a normal rotation back to the States of men that had served in Iceland.
The 21st Engineers was a full regiment in `41, The Reg went from the US direct to the Invasion of North Africa in Nov `42 & serve in NoAf, & Italy for the war.
2 Companies of this Regiment did go to Iceland in `41
I find nothing on a 21st Eng Const BN (separate).
Now for Iceland:
On & July `41, 2 Companies of the 21st Eng Aviation Regiment landed at Rykjavik, Iceland with the first group of Task Force 4 of the 33 Pursuit Squadron.
These 2 Companies were soon redesignated as the 824th EAB.
The second group of Task Force 4 landed 16 Sept `41 and include 2 Battalions of the 5th Eng Combat Regiment.
The 7th Eng Combat Battalion, organic to the 5th Infantry Div. landed in May `42.
Any part of the above units could have landed in Jan when your granddad did.
for now, here is a website for the IX Engineer Command that has a tremendous amount of information on Eng Aviation units including monthly operation reports & histories:
Ok, here is a high dollar question. You mentioned that 2 Companies of the 21st went to Iceland and then redesignated to the 824th EAB. what 2 companies were they and is it possible another company or relief of the soldiers of those two companies were on board such as my grandfather enrout on the 15 Jan 1942 to Iceland. were they Companies or battalions?