Answer by taking a quote from the following article:

George Herbert Walker Bush (born June 12, 1924) is an American politician who served as the 41st President of the United States from 1989 to 1993. Prior to assuming the presidency, Bush served as the 43rd Vice President of the United States from 1981 to 1989. A member of the Republican Party, he had previously been a Congressman, Ambassador and Director of Central Intelligence. While active in the public sector, he was known simply as George Bush; since 2001, he has often been referred to as George H. W. Bush, Bush the Elder or George Bush Senior in order to distinguish him from his eldest son, George W. Bush, the 43rd president of the United States.

The United States was drawn into World War II when the Empire of Japan attacked Pearl Harbor on December 7, 1941. Six months later, Bush enlisted into the US. Navy immediately after he graduated from Phillips Academy on his eighteenth birthday. He became a naval aviator training for aircraft carrier landings and takeoffs on the USS Sable. After completing the 10-month course, he was commissioned as an ensign in the United States Naval Reserve at Naval Air Station Corpus Christi on June 9, 1943 (just three days before his 19th birthday), which made him the youngest naval aviator to that date.  In September 1943, he was assigned to Torpedo Squadron (VT-51) as the photographic officer. The following year, his squadron was based on USS San Jacinto as a member of Air Group 51, where his lanky physique earned him the nickname "Skin". During this time, the task force was victorious in one of the largest air battles of World War II: the Battle of the Philippine Sea.  After Bush's promotion to Lieutenant (junior grade) on August 1, 1944, San Jacinto commenced operations against the Japanese in the Bonin Islands. Bush piloted one of four Grumman TBM Avenger aircraft from VT-51 that attacked the Japanese installations on Chichijima. His crew for the mission, which occurred on September 2, 1944, included Radioman Second Class John Delaney and Lieutenant Junior Grade William White. During their attack, the Avengers encountered intense anti-aircraft fire; Bush's aircraft was hit by flak and his engine caught on fire. Despite the fire in his aircraft, Bush completed his attack and released bombs over his target, scoring several damaging hits. With his engine ablaze, Bush flew several miles from the island, where he and one other crew member on the TBM Avenger bailed out of the aircraft; the other man's parachute did not open. Bush waited for four hours in an inflated raft, while several fighters circled protectively overhead until he was rescued by the lifeguard submarine USS Finback. For the next month, he remained on Finback and participated in the rescue of other pilots. Several of those shot down during the attack were executed, and their livers were eaten by their captors.  In November 1944, Bush returned to San Jacinto and participated in operations in the Philippines until his squadron was replaced and sent home to the United States. Through 1944, he flew 58 combat missions for which he received the Distinguished Flying Cross, three Air Medals, and the Presidential Unit Citation awarded to San Jacinto.  Because of his valuable combat experience, Bush was reassigned to Norfolk Navy Base and put in a training wing for new torpedo pilots. He was later assigned as a naval aviator in a new torpedo squadron, VT-153, based at Naval Air Station Grosse Ile, Michigan. The unconditional surrender of Japan was announced on August 15, 1945. Bush was honorably discharged the following month.

What was his rank?
After Bush's promotion to Lieutenant (junior grade) on August 1, 1944,