was mated with nuclear propulsion. That development produced  a  virtually  invulnerable  missile-firing submarine.  Today,  the  missile-firing  submarine constitutes one of the highest priority elements of the United States’ deterrent capability; that is, a deterrent to nuclear conflict. Each Polaris submarine could launch 16 two-stage ballistic missiles powered by solid-fuel rocket motors, containing a self-contained inertial guidance system. The  Polaris  provided  a  combined  explosive  power greater than the total of all the bombs dropped by all aircraft  during  World  War  II.  Nuclear  propulsion enabled these Polaris submarines to remain on patrol for extended periods, hidden beneath the surface of the sea, ready to launch their missiles. On  station,  a  Polaris  submarine  maintained complete radio silence, receiving radio messages while submerged, but not transmitting to prevent giving away its location. Each ship had two complete crews, the Blue and the Gold, of about 130 people each. The Polaris operated on a system that reflected a major change in the Navy’s traditional ship-manning methods. The crews a l t e r n a t e d    o n    a p p r o x i m a t e l y    3 - m o n t h - l o n g deployments, providing maximum on-station time for the submarine. Its endurance was limited only by the limitations of its personnel. Submarines  were  followed  by  the  world’s  first nuclear-powered  surface  warships.  They  were  the guided-missile cruiser USS Bainbridge, launched April 15, 1961; the guided-missile cruiser USS  Long Beach, commissioned September 9, 1961; and the carrier USS Enterprise,  commissioned  November  25,  1961.  On October 3, 1964, those three ships ended Operation Sea Orbit, a 64-day long, around-the-world, unreplenished cruise. It was during this time that space exploration (fig. 5-15) began. The  Vanguard, a 3 ½-pound payload, was developed  by  the  Naval  Research  Laboratory.  On March 17, 1958, it was placed into orbit to test a system designed  to  launch  earth  satellites  during  the international geophysical year (IGY). Now the oldest man-made satellite in orbit, it is expected to remain aloft for 2,000 years. N ava l   o ffi c e r s   a l s o   p a r t i c i p a t e d   i n   s p a c e exploration. On May 5, 1961, Commander Alan B. Shepard, Jr., made America’s first suborbital flight. The 15-minute shot in   Freedom   7 went 116.5 miles into space. VIETNAM Although the United States was at peace following the Korean Conflict, events were building that would plunge the country into another conflict. Since 1959, the French had been involved in fighting in a country most Americans had never heard of—Vietnam. Americans were introduced to Vietnam in 1965. In that year, the United States entered the Vietnam Police Action. This police action, which caused conflict at home as well as on the battlefield, lasted until January 1973.  Figures  5-16,  through  5-19  commemorate American actions in Vietnam. The  Navy’s  operations  in  support  of  South Vietnam’s  struggle  against  communist  military aggression  consisted  mainly  of  gunfire  support  and carrier aircraft operations. These operations included coastal interdiction patrols against North Vietnamese ships moving troops and supplies to the south. They also included riverine operations by a swarm of various types of patrol craft in the maze of waterways in South Vietnam’s delta area. (By early 1972 all boats and the responsibility for delta operations had been turned over to  the  South  Vietnamese  Navy.)  Naval  construction battalions (Seabees) built several military bases and constructed  water  and  sanitary  facilities  for  local communities. Often, as in World War II, they engaged in fighting as they worked. Navy medical personnel served in the field with Marine Corps and Seabee units, as they did in World War II and in the Korean Conflict. They often  performed  their  duties  under  fire  and  often sacrificed  themselves  to  protect  their  charges  from further harm. As in previous wars, U.S. Navy service and amphibious forces transported over 90 percent of the  personnel  and  supplies  used  in  support  of  that conflict. During the Vietnam era, five new attack carriers j o i n e d   t h e   f l e e t ,   i n c l u d i n g   t h e   wo r l d ’s   fi r s t nuclear-powered carrier, USS  Enterprise  (CVN 65). Vietnam was a different kind of war, a war in which the Navy’s role was ever changing. The Navy used both new and old aircraft—OV-10 Broncos, propeller-driven 5-28 Student Notes: