The U.K. is reportedly lobbying Congress in support of a controversial new warhead for Trident missiles, claiming it’s critical for “the future of NATO as a nuclear alliance.”

According to the Guardian, a letter sent in April from Britain’s Defence Secretary Ben Wallace pushed for the initial spending on the W93 — the first genuinely new U.S. nuclear weapon designed and manufactured in decades.

It also draws the U.K. into the political debate that pits the Trump administration against Democrats and arms control groups over whether the $14 billion program is even necessary for the Navy’s submarine-launched Trident missiles.

The U.K. is supporting the administration’s efforts to speed up work on the warhead and a surprise $53 million request for initial weapon design work in the 2021 budget, the Guardian reported.

“These are challenging times, but it is crucial that we demonstrate transatlantic unity and solidarity in this difficult period,” Wallace told members of the House and Senate armed services committees, the Guardian reported.

“Congressional funding in [2021] for the W93 program will ensure that we continue to deepen the unique nuclear relationship between our two countries, enabling the United Kingdom to provide safe and assured continuous-at-sea deterrence for decades to come.”

Wallace added: “Your support to the W93 program in this budget cycle is critical to the success of our replacement warhead program and to the long-term viability of the U.K.’s nuclear deterrent and therefore, the future of NATO) as a nuclear alliance.”

Initial funding for the warhead was approved by both committees and then temporarily blocked by the House energy and water subcommittee, Defense News reported last month.

“We’ve never had a letter of this sort before, so it was a little bit surprising that this is the issue that they chose to weigh in on,” an unnamed congressional told the Guardian.

Britain and the United States share the same missiles and coordinate work on warheads. The current UK Trident warhead, the Holbrook, is very similar to the W76 warhead, one of two the U.S. Navy uses in its own Trident II missiles, the Guardian reported.

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