1) Spanish boy name 
USS Segundo was an American Balao Class submarine of 1525 tons displacement launched in 1944. USS Segundo was powered by diesel engines providing a top speed of 21 knots, carried a complement of 75 and was armed with one 4-inch gun, two 20 mm Oerlikon anti-aircraft guns; six 21 inch bow torpedo tubes and four 21 inch stern torpedo tubes.
The second-in-command of a large party or company