The Prime Minister was told about last year's Trident missile test when she came into office, Downing Street has confirmed.
Theresa May's official spokeswoman declined to confirm or deny reports a missile malfunctioned during the test, saying only that the PM was told the operation was completed successfully.
Mrs May refused to answer questions on Sunday over what she knew about the test, amid claims there has been a cover-up of the incident.
The Sunday Times reported at the weekend that a Trident II D5 missile veered off course after being launched from HMS Vengeance off the coast of Florida in June.
The timing of the failure is significant because it happened weeks before Parliament voted to spend £40bn on new Trident submarines.
Mrs May's official spokeswoman told reporters at a regular Westminster media briefing that the PM was briefed on the "demonstration and shakedown" operation undertaken by the submarine on its return to service after a refit.
She was told the operation was successful, allowing Vengeance and its crew to return to service.
The spokeswoman went on to say that the Government did not publicly discuss the operational details of these kind of exercises.
When asked whether Mrs May had been told of the result of the test before the Commons vote, her spokeswoman said: "The Defence Secretary and the Prime Minister are routinely informed when one of these specific 'demonstration and shakedown' operations are planned and on the outcome of them.
"In this instance, that was in June so it was under the then prime minister (David Cameron). On taking office, the current Prime Minister was briefed on a range of nuclear issues, including this."
The spokeswoman did not say whether the PM was told about a malfunction in the missile system, saying it was not Government policy to talk about the operational details of tests in public, and told journalists she did not "accept the premise of the question".
"We have been clear that the submarine and the crew were successfully tested and certified," she said.
"That was the purpose of the operation.
"What is also clear is that the capability and effectiveness of the Trident missile is unquestionable."
The Speaker John Bercow has granted an urgent question from Labour's former defence minister Kevan Jones, meaning Defence Secretary Michael Fallon will be forced to come to Commons to face questions on the issue.
A member of David Cameron's media team has told Sky News it was "entirely false" to suggest the former prime minister had been involved in any sort of cover-up.
Conservative MP Dr Julian Lewis, who chairs the Defence Select Committee of MPs, told Sky News the blame for the alleged cover-up rested with Mr Cameron and not his successor in Downing Street.