Simon Oakland campaigned hard to play the lead role and even told director John Flynn that he would do it for no salary. However, Rod Steiger was ultimately cast instead because he was a bigger name at the time.
In 1952, that 20 year pension of $125 a month that Pop talked about getting when he retires translates to about $1,188.00 a month in 2019 dollars.
John Phillip Law said that filming was on the cusp of the new rating system and scenes had to be shot multiple ways. The scene where Rod Steiger grabs him and kisses him was shot and one where he just gives him a hug was shot for television.
Warner/Seven Arts had just done Spiegelbild im goldenen Auge (1967) about a hard-nose military man/veteran infatuated with a young male Private. That role was played by Marlon Brando, who famously played Rod Steiger's brother in Die Faust im Nacken (1954).
The comment stating uniform requirements for off duty soldiers in France is not entirely correct. It is true that the overall commander which would be 7th Army, sets the policy for off-duty troops but it is not an "either or" situation. The situation in France in 1960 was such that military personnel were permitted to wear either civilian attire or the Class A uniform while off duty and in town. Most chose not to wear the uniform. In the time frame of the movie, there was sporadic communist activity in France. At times, troops were ordered not to wear the uniform in town because of this but other than that, the Army left the choice of attire up to the individual.