During the month of December 1967 the ballistic missile submarine, USS George C. Marshall SSBN-564, collided with a Soviet submarine while submerged on patrol in the Mediterranean Sea. The damage was severe enough to prompt an immediate abort of Marshall’s mission and the submarine returned to Rota, Spain.

USS Canopus AS-34, home ported in Rota, was serving as flagship and tender for Submarine Squadron 16 and the task fell to Canopus’s Repair Department to assess the damage to Marshall and recommend a disposition of the same. The Marshall pulled alongside Canopus but the damage was not readily visible because it was all located below Marshall’s surfaced waterline. Canopus’s divers were sent down for a look and to take photographs of the damaged area. The information they gathered was not encouraging.

Marshall had a large gash in the outer shell plating of two starboard ballast tanks that measured approximately sixteen feet in length by approximately five feet at the widest point. The heavy ballistic steel bulkhead that separated the two ballast tanks also sustained a large V shaped tear in it. A set of large, high-pressure air flasks mounted inside the ballast tanks along with their high-pressure piping had been ripped out of their foundations.

Since all the damage was located beneath the submarine’s surfaced waterline a dry-dock was required for any repairs that were to be accomplished. This presented a further problem because SubRon 16’s floating dry-dock, the Oak Ridge ARDM-1 was itself in dry-dock in Cadiz, Spain for overhaul. None of the commercial dry-docks in the area could be used due to security problems and returning Marshall to the States in it’s condition was out of the question.

Canopus’s Repair Department Shipfitters recommended fabricating a cofferdam that could be secured to the hull of the Marshall, the water could then be pumped out and repairs made to the damaged area of the submarine. This plan was approved and work commenced on the 20th of December 1967.

Due to the size of the finished cofferdam the decision was made to fabricate it on Canopus’s helicopter deck. This also provided a staging area for the receipt of the large quantities of material required for repairing Marshall’s damaged ballast tanks. When fabrication of the cofferdam was complete, Canopus Riggers, using the Squadron’s floating crane, hoisted the cofferdam and placed it on the side of Marshall. Canopus Divers, using wire straps and chain hoists secured the cofferdam to Marshall’s shell ensuring a watertight fit.

With the cofferdam securely in place and it and the Marshall’s damaged ballast tanks de-watered, the task of repairing the damaged structure and shell plating began. The HP air flasks were removed and the damaged piping repaired and capped. The damaged structure, shell plating and bulkhead were cropped out and replaced to as-built conditions in accordance with Marshall’s engineering drawings.

After working around the clock beginning the 20th of December, Canopus completed their task on the 17th of January 1968 enabling USS George C. Marshall to return to sea to complete its patrol.

Citation: Reference found in the appendix of the book, Blind Man’s Bluff: The Untold Story of American Submarine Espionage by Sherry Sontag, Christopher Drew, Annette Lawrence Drew

Note from Richard Retin: For this amazing engineering effort, among many others over its 30 years of service, I consider it a point in fact that "the Canopus was the ship that could build or repair anything".