This is not uncommon in the military, and happened long before Covid and the jab. Young healthy men and women going through the rigors of military level training, occasionally just die for no apparent reason...kind of like crib death.
The physical and mental stresses they undergo can be overwhelming...even when they have gone through extensive health screening beforehand. Sometimes there’s an underlying medical condition that wasn’t detected, many times not. It’s very tragic, but also inevitable considering what the military does.
Sure, the vax was safe and effective. You should learn to trust your gummit.
There’s a growing body of evidence that SIDS is caused by vaccines...imagine that.