Over time, the military physical fitness tests have evolved. Specifically, it has shifted its focus to tactical fitness and resilience training. Despite all these changes, some techniques remain timeless and are still implemented in the different physical fitness tests today. Some of these timeless military physical fitness test techniques come from the Navy Basic Underwater Demolition and SEAL Training in the 1970s. For example, the calisthenics used before is still integrated with the training techniques nowadays.
Source: https://www.military.com/military-fitness/spec-ops-recruiting-history-old-school-grinder-pt