Labour's Emily Thornberry 'wrong' over Trident review
The shadow foreign secretary said the UK needed to keep updating its defence policy and make sure any war would be "fought on 21st century terms".
But Ms Griffith said Labour's defence policy was her responsibility and not Ms Thornberry's.
Speaking on BBC's Newsnight she said the party was "fully committed" to having a nuclear deterrent and that the defence review would look at how a Labour government would spend money.
"What it is not about is actually questioning whether we would have a Trident nuclear deterrent because we settled that last year," she added.
Asked if Ms Thornberry was wrong, Ms Griffith went on: "Indeed. Last year we looked at it, in particular, at the national policy forum and it was decided that we would keep the nuclear deterrent."
The shadow defence secretary also distanced herself from Jeremy Corbyn's stance on the potential use of nuclear weapons and the commitment to the Nato principle of mutual defence.
The Labour leader - a long-standing opponent of nuclear weapons - has previously said he would never launch a "first strike" attack as prime minister.
He has also said he would not "automatically" send UK troops to support a fellow Nato member which came under attack.
Ms Griffith said for the nuclear deterrent to be effective it was necessary that "you are prepared to use it", including a first strike policy if required.
She also said Labour was "fully signed up" to Article 5 of the Nato treaty - which commits member states to collective defence.
She told Newsnight there would be diplomatic processes but "ultimately you have to back up your defence and your support" of Nato allies.
Mr Neill said: "Jeremy Corbyn and Emily Thornberry want to disarm Britain and put our security at risk. Corbyn's coalition of chaos would scrap Trident, abandon our allies and would rather talk to Daesh [so-called Islamic State] than strike its barbaric leader."
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