The firm beat off fierce competition to get the contract to construct the 'hunter killer' anti submarine ships.
The new fleet will become the backbone of Australia's defence and is the biggest naval construction project the country has undertaken since World War Two.
Theresa May hailed today's news saying it is the 'perfect illustration' of the deals Brexit Britain will be striking.
She said: 'The sheer scale and nature of this contract puts the UK at the very forefront of maritime design and engineering and demonstrates what can be achieved by UK industry and Government working hand-in-hand.
'We have always been clear that as we leave the EU we have an opportunity to build on our close relationships with allies like Australia. This deal is a perfect illustration that the Government is doing exactly that.
'And while this is an enormous boost for the UK economy, it will also cement our strategic partnership with one of our oldest and closest friends for decades to come.'