The British Defence Ministry initiated orders recently for the nuclear core reactors for its planned next generation of ballistic missile submarines.

The $1.7 billion contract to Rolls Royce covers $940 million for the procurement of reactor cores for the next generation Trident sub, as well as for the final vessel in the Astute-class of attack submarines, the Defense Ministry said.

An additional $783 million will go to modernizing the company’s nuclear reactor production facility in Derby, England to extend its lifetime operation by more than 40 years, the ministry said.

“Having balanced the (Ministry of Defence’s) books we can now invest in vital strategic capabilities to meet the present and future defence needs of the U.K.,” Defence Secretary Philip Hammond said in a statement.

Hammond signaled the contract was forthcoming during an interview with BBC over the weekend. He said even though a final decision on whether to proceed with building the Successor-class, which is to replace the current Vanguard-class of Trident missile carryings subs, will not take place until 2016, it was necessary to begin ordering long-lead items, he said.

“What we’re doing at the moment is ordering the things that have to be ordered now,” he told BBC. He said the Vanguard-class will start coming out of service by the end of the next decade–about the same time the United States plans to start retiring its Ohio-class fleet of ballistic nuclear-powered subs.

Hammond acknowledged that there are differences within the Conservative-Liberal Democrat coalition on building the Successor class, but said for now the plan is to move ahead with the next generation subs pending a final decision in four years.

“The government’s policy is very clear: We are committed to maintaining a credible nuclear deterrent,” he said on BBC.