I wouldn't put it past Teddy Roosevelt. When he was undersecretary of the navy that helped start the Spanish American war he resigned (despite his superiors asking him not to) to fight in the war. He also asked to fight in WW1 despite being old.

For all his positive attributes former senator McCain was known as a hawk. There have always been men who after fighting come away with a firm belief in military power. If you made service a requirement you wouldn't necessarily get fewer hawks just ones you can't criticize for not participating in war themseu