A lot of players were out for a week or two with sprained knees, ankles, etc., after the Navy or Air Force games.
The last time I can recall someone ever getting lost for the season, was in 2014, when Joe Schmidt was engaged with a blocker, and another Navy player dove at his ankles.
The only reason why it wasn't called a chop block, is because the first blocker had released his hold on Schmidt literally a fraction of a second before the diver broke and dislocated his ankle.
Navy was notorious for doing that, and would hold onto the defender (almost never getting called for it) so that the defender couldn't avoid getting chopped down by the diver.
This was a similarly scary play to the one that took out Eric Jones in 1991, when we played against Air Force. The only thing holding Jones' foot to his leg was the skin, given the severity of the break.
Thankfully, now that the rules for cut blocking have changed, that took a lot away from Navy's forte.