Background: Born in Brockton, Massachusetts, to a Jewish family, Davis' father, Louis Davis, worked in a variety of trades in Massachusetts; having found some success in the garment manufacturing field, he moved to Brooklyn in 1934 with his wife, Rose, and two sons, Jerry and Allen. Louis Davis rented a sixth-floor walkup for his family off Utica Avenue, became very successful in the garment trade, and put his two sons through college before seeking a more comfortable dwelling in Atlantic Beach. Although there are a number of stories extant of Louis Davis backing his younger son in anything so long as the boy did not get caught or back down from a confrontation, most of these stories derive from Al Davis. Childhood friends depicted him as more of a talker than a fighter, though very good with his mouth.
Context: Early in the 1962 season, Davis spoke with Oakland Raiders owner F. Wayne Valley about their head coaching job. However, Davis was not then interested. After the team's disastrous 1962 season, in which it lost its first 13 games before defeating a Boston Patriots team demoralized from having just been eliminated from playoff contention, Valley sought to replace head coach Red Conkright.  A number of names were rumored to be in contention for the Raiders head coaching job, from Green Bay Packers coach Vince Lombardi to Lou Agase, former coach of the Canadian Football League Toronto Argonauts. On January 1, 1963, Davis met with Valley and the other Raiders general partner, Ed McGah. According to witnesses present at the negotiations, Davis did not have a high opinion of Valley and McGah, indicating during their absence that they did not know the right questions to ask. They offered him a one-year contract as head coach. He declined, insisting on a multiyear deal as both head coach and general manager, with complete control over football operations. They settled on three years at a salary of $20,000 per annum. According to Davis biographer Ira Simmons, the date that Davis came to Oakland, January 18, 1963, "was probably one of the three or four most important dates in AFL history. Maybe NFL history too." Valley later stated, "we needed someone who wanted to win so badly, he would do anything. Everywhere I went, people told me what a son of a bitch Al Davis was, so I figured he must be doing something right."  The Raiders team had been a late addition to the original AFL in 1960; the franchise had been awarded when the owners of the AFL Minnesota team had been induced to join the NFL instead. While it inherited the departed Minnesota team's draft picks, it had little else. The franchise, originally nicknamed the Senors (changed to Raiders after columnists raised objections) was not established until the other AFL teams had had the opportunity to sign players and coaches, a handicap which contributed to it being the only team to post a losing record in each of the AFL's first three seasons. The University of California refused to let it play at Memorial Stadium in Berkeley, and no other facility in the East Bay was suitable even for temporary use, forcing it to play its first two seasons at Kezar Stadium and Candlestick Park, both located across the bay in San Francisco.  Valley and his group purchased the Raiders in 1961. Valley and his partners used the threat of leaving to induce city officials to construct Frank Youell Field, a temporary facility in downtown Oakland next to the Nimitz Freeway which held about 15,000 people, the use of which was shared with high schools. Planning for a larger stadium -- what became the Oakland Coliseum -- began, but there was no guarantee that it would ever be built.
Question: how long did he hold that position?

Answer: