POSTCARDS PURCHASED IN NEW LONDON, CONNECTICUT, MAY, 1960   Upper State Street, New London, Conn., presents a panorama of the old city (settled in 1646) and the new, a busy metropolis and the home of Connecticut College for Women, the United States Coast Guard Academy and Submarine Base, Mitchell College, Admiral Billard Academy, and of course Ocean Beach Park, Connecticut's leading summer resort. Looking east from the County Court House we see the famed Mohican Hotel, and at the very end of the street the historic Soldiers' and Sailors' Monument.   Submarine Base, New London, Conn., as seen across the Thames River where her submarines engage in training activities . . . on the left is the diving tower, or Submarine Escape Training Tank, towering 134 feet over the landscape . . . on the right, some of the workshops and office buildings which make this the largest submarine base in the world.   The Submarine Base, New London, Conn., is our nation's only submarine school, and is also the largest submarine base in the world. Students here gain important practical knowledge on training missions which leave every morning heading down the Thames River towards Long and Block Island Sounds.   The Submarine Base at New London, Conn., is the largest submarine base possessed by any navy. It is the operating base for two submarine squadrons and is the location of the Headquarters of the Commander, Submarine Force, U.S. Atlantic Fleet . . . The "Guppy" is a new fleet type submarine, following streamlining to increase underwater speed. (Official U.S. Navy Photograph.)   "Guppy" Submarine at the Submarine Base, New London, Conn., is one of our fleet type submarines, streamlined to increase underwater speed. This Submarine Base is the largest possessed by any navy in the world.   The Submarine Escape Training Tank at the Submarine Base, New London, Conn., is the only such diving tower in the United States. Commissioned in 1930, this 134-foot steel structure is used by the Navy for training and experimental purposes.