The cost of modernising ageing planes, ships and missile silos that make up the nuclear arms would cost 50% more than if the US only operated and maintained its current equipment in the field, the CBO concluded. 

The CBO reviewed the Obama administration’s plans for modernisation of the nuclear arsenal. 

Donald Trump has directed his secretary of defence James Mattis to conduct his own review of the nuclear forces, which is expected to be published in the coming months.

More than $800bn of the cost would be to operate and sustain nuclear forces and about $400bn to modernise them, the report said. 

It also found during the “peak years of modernisation”, the annual costs of nuclear forces could roughly double the current amount and nuclear forces would have to compete with other defence priorities for funding. 

Speaking of the Obama Administration plans, US house armed services committee member Adam Smith said: “Congress still doesn’t seem to have any answers as to how we will pay for this effort, or what the trade-offs with other national security efforts will be.”

Costs would increase from $29bn in 2017 to $47bn in 2027, before rising to around $50bn a year through the early 2030s, the report said. 

Mike Pence, the US vice-president, said last week that the Trump administration “is committed to strengthen[ing] and modernis[ing] America’s nuclear deterrent”.