Labour leader Jeremy Corbyn is braced for a potentially fiery showdown with his top team over the renewal of Trident.
The shadow cabinet is due to discuss the nuclear deterrent for the first time when it meets later.
Shadow defence secretary Emily Thornberry gave the group a brief outline of her thinking last week, but substantive debate on the party's approach to the looming Commons vote was delayed.
Mrs Thornberry, who favours unilateral disarmament, was branded "waffly and incoherent" after she spoke to MPs and peers about the issue at a meeting on Sunday.
She told the Parliamentary Labour Party (PLP) meeting she wanted to carry out the ongoing review of Labour policy on Trident in an "atmosphere of mutual trust and respect".
In the face of hostile questions from MPs and peers, Mrs Thornberry said: "There is no point trying to shout me down."
Some MPs told reporters outside the room afterwards that she had compared the Trident system to Spitfire aircraft.
But a senior Labour source insisted she had been trying to suggest that some military technology had to be replaced, like Spitfires, and others could be updated - like Tornadoes.
The source indicated that Mrs Thornberry had also raised doubts about whether submarines were a safe way to carry the nuclear deterrent.
"She was talking to some people about drones and it was apparent it was absolutely possible that large submarines could be tracked and attacked by drones," the source added.
Interventions were "evenly" split between speakers who wanted to renew Trident, those who did not think it was a "binary choice", and those who opposed renewal, according to the source.
Quizzed on how it had gone as she left the meeting, Mrs Thornberry said: "All right."
When former leader Lord Kinnock was asked for his verdict on her performance, he replied "Yeah", then walked away laughing.
Former shadow defence minister Kevan Jones said she had taken questions "but didn't answer any", adding: "Waffly and incoherent."
Mr Corbyn was not present as he was manning a phone bank for Labour's London mayoral candidate Sadiq Khan, but he is expected to attend the next PLP meeting in two weeks' time.