Lieutenant commander (United States) in the context of Commander (United States)

Little Boy was a type of atomic bomb created by the Manhattan Project during World War II. The name is also often used to describe the specific bomb (L-11) used in the bombing of the Japanese city of Hiroshima by the Boeing B-29 Superfortress Enola Gay on 6 August 1945, making it the first nuclear weapon used in warfare, and the second nuclear explosion in history, after the Trinity nuclear test. It exploded with an energy of approximately 15 kilotons of TNT (63 TJ) and had an explosion radius of approximately 1.3 kilometres (0.81 mi) which caused widespread death across the city. It was a gun-type fission weapon which used uranium that had been enriched in the isotope uranium-235 to power its explosive reaction.

Little Boy was developed by Lieutenant Commander Francis Birch's group at the Los Alamos Laboratory. It was the successor to a plutonium-fueled gun-type fission design, Thin Man, which was abandoned in 1944 after technical difficulties were discovered. Little Boy used a charge of cordite to fire a hollow cylinder (the "bullet") of highly enriched uranium through an artillery gun barrel into a solid cylinder (the "target") of the same material. The design was highly inefficient: the weapon used on Hiroshima contained 64 kilograms (141 lb) of uranium, but less than a kilogram underwent nuclear fission. Unlike the implosion design developed for the Trinity test and the Fat Man bomb design that was used against Nagasaki, which required sophisticated coordination of shaped explosive charges, the simpler but inefficient gun-type design was considered almost certain to work, and was never tested prior to its use at Hiroshima.

USS Johnston (DD-557) was a Fletcher-class destroyer built for the United States Navy during World War II. She was named after Lieutenant John V. Johnston, an officer of the US Navy during the American Civil War. Johnston was laid down in May 1942 and was launched on 25 March 1943. She entered active duty on 27 October 1943 under the command of Lieutenant Commander Ernest E. Evans and was assigned to the US Pacific Fleet. Johnston provided naval gunfire support for American ground forces during the Gilbert and Marshall Islands campaign in January and February 1944 and again, after three months of patrol and escort duty in the Solomon Islands, during the recapture of Guam in July. Thereafter, Johnston was tasked with escorting escort carriers during the Mariana and Palau Islands campaign and the liberation of the Philippines.

On 25 October 1944, while assigned as part of the escort to six escort carriers, Johnston, two other Fletcher-class destroyers, and four destroyer escorts were engaged by a large Imperial Japanese Navy flotilla. In what became known as the Battle off Samar, Johnston and the other escort ships charged the Japanese ships to protect nearby US carriers and transport craft. After engaging several Japanese capital ships and a destroyer squadron, Johnston was sunk with 187 dead, including Evans. Johnston's wreck was discovered on 30 October 2019 but was not properly identified until March 2021. Lying more than 20,000 feet (6,100 m) below the surface of the ocean, it was the deepest shipwreck ever surveyed until the 22 June 2022 discovery of USS Samuel B. Roberts, sunk during the same engagement.

In the United States Army, Marine Corps, Air Force and Space Force, major is a field officer above the rank of captain and below the rank of lieutenant colonel. It is equivalent to the rank of lieutenant commander in the Navy and Coast Guard. Although lieutenant commanders are considered junior officers by their services, majors are senior officers.

The pay grade for the rank of major is O-4. The insignia for the rank consists of a golden oak leaf, with slight stylized differences between the versions of the different services. Promotion to the rank of major is governed by the Department of Defense policies derived from the Defense Officer Personnel Management Act of 1980.