An icebreaker leased to Shell sprang a leak and had to return to Dutch Harbor early Friday morning. The MV Fennica carries the company’s capping stack — a critical piece of safety equipment for Shell’s plan to drill two wells this summer in the Chukchi Sea.

Coast Guard spokesman Shawn Eggert says the ship’s crew noticed the problem around 3 a.m.

“The Motor Vessel Fennica was departing from the port of Dutch Harbor, Alaska when the crew discovered that they had water coming in to their Port No. 4 ballast tank. At that point they returned to port and tied up at the Delta Western dock,” he said. “Divers there discovered a one-inch wide by three foot long fracture in the ship’s hull.”

Eggert says the Coast Guard has begun an investigation into the cause and will examine Shell’s proposal to repair the ship. The spokesman says a marine pilot, an expert in local navigation who maneuvers a vessel as it leaves or enters a port, was on board at the time the breach was discovered.

Shell did not respond to requests for an interview but a Shell spokesman, in an email, describes it as a “small breach.” He says the vessel was in charted waters at the time. Whether the damage will delay Shell’s plans for the already short Arctic drilling season is unclear. The spokesman says that will depend on the extent of the required repairs.

If the final permits for the Chukchi operation are approved, the government would require Shell to have the Fennica nearby, with the capping stack ready to deploy within 24 hours of a blowout. The Fennica is a 380-foot Finnish-owned multipurpose icebreaker. Shell is also leasing its sister ship, the Nordica, for ice management.

If Shell is able to return to the Chukchi, it will be the first time since its 2012 season, which was plagued with shipping and towing problems.