Emily Thornberry angers Labour MPs by comparing Trident to the Spitfire
She made the remarks at a stormy meeting of the Parliamentary Labour Party in the House of Commons.
Ms Thornberry, who is opposed to Trident renewal, was updating her fellow MPs on the progress of the defence policy review she is leading.
She told them: "We want to be able to work together on (the question of Trident renewal) and come to a collective decision. We all have different views, but I would ask people not to go into entrenched positions on this and to look at the evidence."
At one point, she was forced to say "there's no point trying to shout me down" as she was challenged by opponents of unilateral nuclear disarmament.
But it was her comments about Spitfires which caused the most unrest.
One MP told PoliticsHome: "She said that just as we had replaced Spitfires and Tornados have been updated, she was worried about the obsolescence of Trident subs.
"She has basically latched onto the latest conspiracy theory of the anti-Trident lobby, who say drones will be able to track submarines from the air. But Admiral of the Fleet Lord Boyce himself has said that there is as much chance of us putting a man on Mars within six months as there is of the seas becoming permeable in the next 30 years.
"Her comments went down very, very badly. To have come to the view that Trident,the most advanced large manufacturing and engineering project in the world, is like a Spitfire shows that her mind is absolutely closed and she is determined to do Jeremy Corbyn's bidding, which is to give people any reason not to vote with the Government on Trident renewal."
Another MP said: "There were gasps of disbelief in the room over the Spitfire/Trident comparison."
Former defence minister Kevan Jones m who quit Labour's frontbench over Ms Thornberry's appointment, described her performance as "cringe worthy" and "waffly and incoherent".
Madeleine Moon, the Labour MP for Bridgend, appeared to make her unhappiness known on Twitter.
Oh dear oh dear omg oh dear oh dear need to go rest in a darkened room
When she emerged from the meeting, Ms Thornberry insisted the reception she received had been "alright".
A Labour source denied the Shadow Defence Secretary had explicitly compared Trident to a Spitfire.
The source said: "She was talking about drones and about how it was absolutely possible that with improved technology, large submarines could easily be tracked and attacked by drones.
"She said that some technology can last for a long time. We don't have Spitfires any more, but we have Tornadoes, so we should consider all the options."