Lockheed Martin is negotiating a long-term purchase agreement which would insulate it against the effect of proposed new US steel and aluminium tariffs until 2021, chief financial officer Bruce Tanner said on Monday.

In an interview with the Financial Times, Mr Tanner said the company — one of the largest US defence contractors — is discussing an agreement for aluminium for the C130 military transport plane, one of the biggest users of the metal in the Lockheed portfolio but which represents only about 2 per cent of sales. The metals “are not a large proportion of our content”, he added.

Even without a long-term contract, the potential hit from the 10 per cent aluminium tariff proposed by President Donald Trump would only be “in the hundreds of thousands of dollars”, a small proportion of the price of planes which sell for $65m to $70m each, he said.