The chief of defence staff is "fully entitled" to speak out in support of Trident, Michael Fallon has said.
The defence secretary said it would be "odd" if Gen Sir Nicholas Houghton did not answer questions about it, following claims he breached the military's political neutrality.
Sir Nicholas said at the weekend that he would be worried if an anti-nuclear view "translated into power".
Labour's Jeremy Corbyn has said he would never press the "nuclear button".
He called on Mr Fallon to "take action" following Sir Nicholas' comments.
The Labour leader accused Sir Nicholas of political bias after he told the BBC's Andrew Marr that refusing to launch nuclear weapons would "seriously undermine" Britain's "deterrent".
Speaking on BBC Radio 4's Today programme, Mr Fallon said that Sir Nicholas had not attacked Mr Corbyn personally and that he had "given a straight answer to a straight question".
"I think he went on immediately to say he wasn't commenting personally on Mr Corbyn's position but he was asked about the nuclear deterrent and he gave an answer and I think he is fully entitled to do that," he said.
Mr Corbyn, a leading member of the Campaign for Nuclear Disarmament, faced criticism from his shadow cabinet at his party's annual conference when he revealed that would not fire Britain's nuclear weapons if he were PM- and he has since praised Scottish Labour's rejection of Trident.