COLOGNE, Germany ― The German Navy’s six-strong fleet of submarines is completely out of commission after the only operational sub had an accident off the coast of Norway on Sunday.

The U-35 was moved into ThyssenKrupp Marine Systems’ shipyard in Kiel after a rudder blade was damaged during a diving maneuver, the newspaper Kieler Nachrichten reported. The submarine was scheduled to participate in exercises in the Skagerrak, the strait between southern Norway, southeast Sweden and Denmark.

The U-35 is a 212A-class boat, the same type that TKMS will build for Norway under a multibillion-dollar deal announced early this year. Italy also operates two boats of the class.

Norway makes decision on submarine order In the fierce competition between the two remaining bidders on a submarine deal, Germany's TKMS beat out France's DCNS.

Exactly how long the U-35 will be out of service was still unknown on Friday. Service officials hope to make an assessment next week about the extent of the damage.

The submarine joins three ships already being overhauled at the Kiel shipyard. German military news service Augen Geradeaus, citing sea service data, reported that the U-31 will be in the yard until December, and the U-33 and U-36 are undergoing maintenance until February 2018 and May 2018, respectively. Additionally, the U-32 and U-34 are out of service and awaiting maintenance spots at the shipyard.

Navy officials blame bottlenecks in the procurement of spare parts for the submarines’ downtime. While a comprehensive package of spare parts was a key aspect of any new acquisition during the Cold War, cost-saving measures adopted since then have resulted in parts no longer being kept in reserve, German Navy spokesman Capt. Johannes Dumrese told the newspaper group SHZ.

According to a statement by the sea service, the most recent acquisitions of the U-35 and U-36 will usher in improved maintenance policies. Irrespective of the U-35′s fate, the Germany Navy expects to have three or four submarines ready for service in mid-2018.