Hank Greenberg
The Tiger star’s lost time to military service actually pre-dated America’s involvement in World War II. Drafted into the Army following the 1940 season, he missed most of 1941, but was prepared to return to the Tigers in 1942 until Pearl Harbor scrambled those plans. Greenberg remained in military service until late in the 1945 seasons, costing him three full MLB seasons and parts of two others.
Greenberg was 30 years old in 1941, and 34 in 1945, so his missed time coordinated with something approaching his prime.
In the three seasons prior to being drafted, Greenberg hit 58, 33, and 41 home runs. In the two full seasons following his 1945 return, he hit 44 and 25, so the dropoff really occurred following the war and not during his lost seasons.
Since Greenberg had produced 40 or more home runs in four of the five seasons before and after the war’s outbreak, projecting that he might have averaged 40 home runs during his missing five near-prime seasons is reasonable.
There’s no guarantee of that, of course. His home run rate did during his two partial seasons, 1941 and 1945, although that could easily be attributed to extenuating circumstances.
Projecting Greenberg for another 40 home runs for each of his five missing or largely missing seasons, the 316 home runs he hit otherwise suddenly elevates Greenberg into the 500 home run class.