Navy SEALs - Radio Operator
A 4-man SEAL fire team during tactical warfare training.
The SEAL with the radio on his back is known as the RTO, which stands for Radio Telephone Operator, something of an old-fashioned military term that has nonetheless stuck.
Wherever they operate, the radio is one of the most vital pieces of equipment that special ops teams carry.
This ia a vintage shot, taken in 1987.
Note the Colt Model 653 M16A1 carbine fitted with an M203 40mm grenade launcher wielded by the RTO.