Mr Williamson set out the threats facing the UK, his vision for the Modernising Defence Programme, and make the case for investment.
It was an eventful cabinet. The big winner today however was the defence secretary - and May ultra-loyalist - Gavin Williamson.
A leaked document suggested dropping the army's historic crest and 'Be the Best' motto over concerns they were elitist.
Earlier, the defence secretary was accused of pursuing a policy that “belongs in a Netflix series.”
"A dead terrorist can't cause any harm to Britain," he added.
The hole in the Ministry of Defence's budget is apparently £1.7bn a year, which could see thousands of armed troops cut.
The Argentine navy announced that a sound thought to be an explosion had been detected by US and specialist agencies leading the search.