Oxford United have apologised for releasing a collection of ‘United 93’ clothing around the 25th anniversary of 9/11.The League One club launched a range of merchandise that included an American football-style shirt that had ‘United 93’ on the back.Oxford have apologised for their ‘United 93’ collection, which they have now removedGettyIt was seemingly intended to reference that Oxford were founded in 1893, when they were initially known as Headington Football Club.However, its release was in close proximity to the 25th anniversary of the September 11 attacks, also known as 9/11, which was last Friday.Terrorist organisation Al Qaeda hijacked and crashed four planes on September 11, 2001, one of which had the call sign United 93.The United Airlines flight left Newark International Airport for San Francisco International Airport, but the hijackers are said to have aimed it towards a federal government building in Washington, D.C.Passengers and crew revolted, but the plane crashed into a field near Shanksville, Pennsylvania, killing 33 passengers, seven crew and the four hijackers.Oxford express ‘sincere apologies’In a statement, Oxford confirmed that they have removed the United 93 clothing and admitted to a lack of sufficient due diligence.It read: “Oxford United would like to sincerely apologise for the recent launch of the Campus Collection.“The range was released without understanding of the historical context and associations. It should not have reached the point of sale and we take full responsibility for not undertaking proper due diligence. “We have removed the collection with immediate effect and are reviewing our approval processes to ensure nothing like this happens again.“Once again, we would like to put on record our sincere apologies for this error and for any offence caused.”View Tweet: https://t.co/BODCzB6yq0United 93 was one of four hijacked planes on 9/11GettyA total of 2,996 people, including 19 terrorists, were killed during 9/11, with thousands also injured.Two planes deliberately crashed into the Twin Towers at the World Trade Center in New York City.Another was flown into the Pentagon, the United States Department of Defence headquarters, in Arlington County, Virginia.Oxford so far this seasonAfter five matches played in League One, Oxford sit sixth with three wins and ten points overall.The U’s, managed by former Arsenal midfielder Aaron Ramsey, are back in the third tier following relegation from the Championship.Oxford host Cambridge United at the Kassam Stadium on Saturday.