Fifteen minutes that stopped a nation
During the MR-3 countdown a number of planned communications checks had been conducted with Shepard on both UHF and HF radio. Then, two minutes prior to the planned liftoff time, the UHF radio was switched on and continuous communications were maintained between Shepard and Deke Slayton, serving as the CapCom in the Mercury Control Center. This ensured that the communications systems were fully operational at the time of launch. Shepard also received voice checks from astronauts Wally Schirra and Scott Carpenter, callsigns Chase One and Chase Two because they were circling the Cape at high level in their F-106 jets in order to follow the rapid progress of the Redstone as it ascended and headed downrange.