Marines with 2nd Reconnaissance Battalion, 2nd Marine Division, prepare to dive and perform underwater knot-tying in a Special Operation Command screener during a pre-dive course at Marine Corps Base Camp Lejeune, N.C., May 25 – June 5, 2015. The students had to tie five knots underwater; having only five separate breathing opportunities with only 30 seconds on the surface of the water between tying each knot. - Marines with 2nd Reconnaissance Battalion, 2nd Marine Division, prepare to dive and perform underwater knot-tying in a Special Operation Command screener during a pre-dive course at Marine Corps Base Camp Lejeune, N.C., May 25 – June 5, 2015. The students had to tie five knots underwater; having only five separate breathing opportunities with only 30 seconds on the surface of the water between tying each knot.