My father (DOB 09/03/1919) entered the army 01/1942. By 12/42 he made Sgt. He was a 1st Sgt. when separated 10/45. Is this unusual?
Uncommon, but not Unusual
The US Army went through a MASSIVE increase in numbers during WWII. In 1942 there were between 1.5 million and 3 men in the US Army. (1.5 in 1941, I believe 3 million by the end of '42, so your Father joined somewhere in there.) That's already a massive increase over the 189,000-odd strong force of 1939, and the army would be 8.2 million men strong by 1945, when he got out. The army was DYING for noncoms. If your dad had a high school/college education and showed even a modicum of ability, he'd likely be promoted straight out of basic. From there his specialization would play a part. Combat arms had rapid promotion, as those who lived stepped into the boots of men who died or were rotated to other units. Combat service/combat service support could also find rapid promotion. Your dad used to be an administrative clerk? Make him a supply Sgt. He knows how to do all the paperwork. Your dad shows some brains and good initiative as a Sgt., regardless of job? Awesome, we're standing up a new unit and his 6 months experience makes him about as qualified as anyone else, give him a 1st Sgt's stripes and send him over! Basic numbers can be found Here
Now if your dad didn't have any special skills, was some no-talent stateside pen-pusher with no desire to move up in the world, going from basic to 1st Sgt in 3 years would be unusual. But given the circumstances of the war promotions came QUICK. To put it in perspective, the 1939 army was 189,000 and change. There was about 1 officer per 13 enlisted men. The US army of 1945 was 8.6 million, and by 1939 numbers needed over 661,538 officers alone (even more because the ratio of officers to men increased substantially). More than 3x the total population of the pre-buildup army. The NCO crunch was even worse. At the start of the buildup NCOs made up about 25% of enlisted. By the end, that number was closer to 50%.Source So if your dad was good at all at his job as a Sgt, making 1st sergeant in 3 years total service wasn't that uncommon a thing.