Amid criticism over her decision to include US-made aircraft, the minister told Sueddeutsche Zeitung newspaper the F-18s were needed as "bridging technology".

To retire the present fleet of Tornado aircraft, the Luftwaffe (air force) must maintain certain capabilities, and she told the German daily "it has to be said, that currently only US manufacturers are offering" the capacity to carry nuclear weapons.

In a letter to parliament's defence committee, the ministry underscored that the Boeing-built jets would allow Germany to meet its NATO nuclear sharing duties as they can carry US atomic warheads.

At present, the European-built Tornado is the only Luftwaffe plane certified to carry nuclear arms.

The letter stressed however that Eurofighters would be the "backbone of the Luftwaffe".

The US-European planes would offer the air force the "best operational advantages and guarantee uninterrupted capabilities".

"At the same time, this decision strengthens the transatlantic partnership and underpins our credibility in the NATO alliance," it read.

- Never pleased -

The purchase order would still require parliamentary approval -- which Kramp-Karrenbauer said would be sought in batches.

The procurement request for the F18s is expected to be put to lawmakers during the 2022-2023 session, according to her letter to the defence committee.

The timeline may be no accident as Chancellor Angela Merkel's junior coalition partner, the centre-left Social Democrats, have voiced unhappiness about the plan to include US-made jets.

The minister had also sparked furore after it emerged that she had spoken to her American counterpart about the potential order before formally informing the SPD or the parliamentary defence committee.

"Nothing has been made transparent to us in any way," defence committee chief Wolfgang Hellmich told the Sueddeutsche Zeitung daily on Monday.

"So far we have received nothing."

The defence ministry argued that operating the Tornado would no longer be economical by 2030, making 2025 the deadline for finding a replacement.

As an advanced Franco-German fighter dubbed the Future Combat Air System (FCAS) is not expected to be ready until 2040, the ministry has had to resort to a US solution.

But a French diplomatic source had told AFP that Paris is "never pleased to see a European partner buy American equipment".

Germany buying the F-18 is judged by France as "less problematic" than the newer F-35, a significantly more expensive alternative that could have called into question Berlin's commitment to FCAS.

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