BERLIN (Reuters) - The German Defence Ministry estimates it will cost nearly 9 billion euros to keep its aging fleet of 93 Tornado fighter jets flying until 2030, according to a classified document provided to German lawmakers this week.

FILE PHOTO - A technician works on a German Tornado jet at the air base in Incirlik, Turkey, January 21, 2016. REUTERS/Tobias Schwarz/Pool

The steep cost forecast includes 5.64 billion euros to maintain the warplanes, which first entered service in 1983, 1.62 billion euros to design replacements for obsolete parts, and 1.58 billion euros to procure them, according to the document, which was viewed by Reuters.

Germany in January decided to pick either the Eurofighter or Boeing Co’s F/A-18E/F fighter jet to replace its Tornado fleet in coming years, dropping Lockheed Martin’s F-35 stealth fighter from a tender worth billions of euros..

But neither the F/A-18 nor the Eurofighter, built by Airbus, Britain’s BAE Systems and Italy’s Leonardo SpA, are currently certified to carry U.S. nuclear weapons, as required under Germany’s obligations to NATO.

That means Germany will be dependent on its Tornado fleet until it gets new certified planes - a process that could take years.

The estimate came in response to a query by lawmakers from the opposition Free Democrats, who have criticized the ministry for dropping the F-35 - the only aircraft already certified.

The ministry did not specify the cost of operating the Tornado fleet until 2035, the current target, despite a specific request to do so from the lawmakers, and said it could adjust the retirement schedule.

Parliamentary sources said the estimate was even higher than expected at around 100 million euros per plane, and it would be cheaper to purchase new aircraft.

However Germany’s sluggish defense procurement process, and the complicated process of certifying new aircraft to carry nuclear weapons, meant any new warplanes were unlikely to enter service until 2025 or even later.

Of Germany’s 93 Tornado jets, 85 are operated by the Luftwaffe, or air force, but not all are equipped to carry nuclear weapons. The remaining planes are used for training.

The current Tornado fleet has a combat readiness rate of under 40 percent, according to sources familiar with new ministry data. Germany in past years had published such data, but this year made the readiness of its weapons a classified matter for security reasons.