LONDON — Design of a new fleet of Royal Navy nuclear missile-carrying submarines has advanced with the award to BAE Systems of a £201 million (US $290 million) contract to complete assessment phase work on the boat.

The cash will allow BAE to develop the design of the submarine, including equipment and systems layout, develop-manufacturing processes, and undertake production of early prototypes, the Ministry of Defence said in a statement released Tuesday.

The next phase of the program, known as Successor, is expected later this year subject to parliamentary approval to renew Britain's nuclear deterrent.

The Conservative government has committed to building four Trident missile-armed submarines to replace the current Vanguard class of boats providing Britain’s nuclear deterrent.

The £201 million deal is the final large design payment to BAE under a £3.3 billion assessment phase package earmarked by the previous government for development of Successor.

The announcement follows three funding packages awarded to BAE: two awards of £328 million and £315 million to commence initial design in 2012, followed by £257 million in 2015 for the detailed design.

Nuclear power plant-builder Rolls-Royce and support company Babcock are also being funded for Successor work.

Further contract awards to the two companies as part of the assessment phase package are possible.

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"The Successor program is one of the most challenging engineering projects in the world today, and this additional funding will enable us to further mature the design." said Tony Johns, the managing director of BAE Systems Submarines.

A spokeswoman for the MoD said the prototyping effort covered by part of the contract award was aimed at ensuring that the design outputs can be used in the intended manufacturing processes

"This will involve the fabrication of some representative samples of the boat's structure, such as diesel fuel tanks, the clean reserve oil tank, the dirty oil tank and a tank for collecting the drains," she said.

The government's strategic defense and security review published in November delayed by several years the introduction of the first of the new submarines to the early 2030s.

BAE had previously said it hopes to start construction this year but it is not clear now when a production contract will be signed.