Why do you use the 1950s as the starting date? Why not the 1930s or 1900s or 1880s? Might it be starting with those years won't support your assertion?
Ooh, he should pick the 1980's as a starting point! I think he'd be pleasantly surprised.
(snip)
BTW, it was my understanding that at least parts of the US armed forces aklready use computer games in training? Notably their own version of Doom?
The US Marines experimented with using Doom as a team tactics training aide, but they never used it widely. It's available for public use, although it's pretty crappy: Marine Doom
The US military does use a few games (some based on commercial video games) as infantry training aides. None are used for "conditioning" or anything like that, they're used for small unit tactics and combined arms training. A few (there are several others, not counting vehicle simulators):
VBS1 (small unit / combined arms based on the game Operation Flashpoint)
VBS2 (upgraded version of the above, similar to the consumer Armed Assault product)
DARWARS: Ambush (designed to train troops on convoy scenarios, not sure if it's actually being used by any service branches)