COLOGNE, Germany – As Germany ponders a suitable successor for the nuclear-capable Tornado aircraft, U.S. government officials are keeping a close eye on the proceedings -- and could have an outsized impact on Germany’s final options.

Among the four competing aircraft types, three are American: the Lockheed Martin F-35, as well as variants of Boeing’s F-15 and F-18.

But officials at the ministry of defense in Berlin are leaning toward a European aircraft, the Eurofighter Typhoon. That is in large part because fielding an improved version of that airplane, developed by a consortium of Airbus, Leonardo and BAE Systems, is considered a stepping stone toward fielding an entirely new type of aerial weapon for the continent in 2040.

The politics around the selection process make the deal worth watching closely. Under a NATO agreement dating back to the Cold War, Germany has outfitted its Tornado fleet with a nuclear option, enabling the planes to carry U.S. atomic bombs eastward in case of a major war between the alliance and the former Soviet Union. Following several waves of reductions, around 20 bombs of the B-61 variant are still believed to be at Büchel air base, situated at the edge of the Mosel river wine region between the cities of Koblenz and Trier.

Whichever plane Germany picks to replace the aging Tornados must be able to continue the nuclear role, the government’s current thinking here goes. And that is where things could get complicated, because the U.S. government gets a say.

Reuters reported in June that German officials had sent a letter to Washington asking what it would take to certify the Eurofighter for the nuclear mission. The process could take anywhere between five to ten years, potentially throwing a big wrench in the Luftwaffe's timing, sources told Reuters.

In contrast, certifying U.S. aircraft to carry U.S. atomic bombs flown by German pilots is expected to be a simpler proposition. Variants of the F-35 are expected to become nuclear-weapons certified in the early 2020s, while the F-15 and F-18 already are presumed to possess the capability.

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German officials have declined to discuss the reported Eurofighter inquiry or anything related to the nuclear capabilities of the envisioned Tornado successor aircraft. And while the U.S. Defense Department has been similarly mum on the issue, a spokesman offered a statement to Defense News that includes something of a nudge.

“The U.S. government is actively engaged with the German Ministry of Defense to identify the requirements for its Tornado replacement program,” spokesman Johnny Michael wrote. He added that the status of ongoing “policy reviews” would be kept private.

“The German Tornado replacement program is a sovereign national decision,” Michael wrote. “We believe that a U.S. platform provides the most advanced, operationally capable aircraft to conduct their mission.”

Government proclamations supporting a country’s own defense companies are nothing new. But the tack is noteworthy in the flare-up between Washington and Berlin over trade policies and defense spending.

Many in Germany still expect the Tornado-replacement debate to be about the relatively mundane mechanics of preserving a decades-old linkage between the United States and Germany. But in the age of Trump, these matters could take a very different turn, argues Christian Mölling of the German Council on Foreign Relations.

“If it was just technical, this would not be an issue,” he said. “But right now everything is political between Germany and the United States.”

President Trump is known for his desire to inject an economic calculus into all sorts of policy debates, and the U.S. leverage over German-carried American nukes may just turn out to become another opportunity to boost American firms. The chief executives of the two American companies in question, Marillyn Hewson for Lockheed Martin and Dennis Muilenburg for Boeing, are known to have Trump’s ear.

Germany fears steeper Tornado costs after the UK ditches its planes German defense officials brace themselves for the reality of maintaining a dwindling fleet of aircraft.

Government leaders here have traditionally clung to the transatlantic nuclear connection as an important means to keep Berlin at the table in strategic matters involving the alliance. But there are also those who believe the agreement is an arcane relic of the Cold War, and that U.S. atomic bombs stationed on German soil are more of a liability than a strategic edge.

The coming Tornado-replacement debate here could once again open that can of worms, especially if Trump moves to make a “business case” out of it to benefit U.S. contractors, said Mölling.

There is one way to table the thorny issue altogether, which has been Germany’s tactic for years. And that involves absorbing the rising price tag of keeping the nuclear-capable Tornados flying -- though that is becoming an increasingly expensive proposition given the fleet’s age.

“There does not have to be a nuclear Tornado replacement,” said Karl-Heinz Kamp, president of the Federal Academy for Security Policy, a government think tank. He noted that any German government is acutely averse to the publicity surrounding Berlin’s would-be atomic bombers.