REUTERS/GETTY Fallon has congratulated Trump's new defence secretary General Mattis

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General "Mad Dog" James Mattis has a "deep understanding" of the military culture shared by the United States and the UK, Defence Secretary Sir Michael Fallon said as he congratulated the nominee. Nicknamed "Mad Dog", the 66-yearold has a distinguished service record and retired in 2013 from the Marine Corps. But he was criticised in 2005 when he declared it was "fun to shoot some people".

President-elect Trump's pick to run the Pentagon, however, will need to win approval in Congress through a special waiver. A law currently bars retired military officers from becoming defence secretary within seven years of leaving active duty. Sir Michael said: "I congratulate General James Mattis on his nomination and wish him well.

"He has a deep understanding of our shared military culture as well as experience of serving alongside British forces. "The US is, and will remain, our closest partner on security and defence. "I look forward to continuing our close co-operation to fight terrorism, deter aggression, and collaborate on innovative technologies to ensure the security of our nations."

REUTERS President Elect Trump has faced backlash after appointing the controversial General Mattis

President-Elect Donald Trump in pictures Tue, December 13, 2016 Donald John Trump is an American businessman and politician who is President-elect of the United States as well as chairman and president of The Trump Organization Play slideshow 1 of 64

At a rally in Cincinnati yesterday Mr Trump said: "We are going to appoint 'Mad Dog' Mattis as secretary of defence." The formal announcement will be made on Monday. Trump has previously described Mattis as "a true general's general".

REUTERS General James Mattis is called by some as ‘Mad Dog’