Submarines: Miami Survives The Heat


September 17, 2012: The U.S. Navy has decided to spend nearly half a billion dollars to repair damage done by a fire on the USS Miami (a Los Angeles class SSN or nuclear attack submarine). The blaze occurred while the sub was in the Portsmouth (Maine) Naval Yard for maintenance and upgrades. Initially the navy estimated that the sub suffered $400 million in damage. But a more detailed examination of the revealed that it would cost at least $450 million.

The fire (set by a deranged shipyard worker) took place last May 23rd and there were fears that the 22 year old Miami might be scrapped. There is some suspicion that the repair bill may be purposely low, as it is much more difficult to cancel a project once it has started, even if the costs begin to mysteriously escalate. Maine politicians are eager to keep the shipyard operating, despite the fact that yard management hired an unstable worker who eventually set two fires (the big one on the Miami and another that was quickly put out). Maine politicians get re-elected, in part, by continuing to get navy contracts to keep these shipyards open. But this effort is now complicated by a defense budget that is shrinking and the navy along with it. The Miami repair project may still get cancelled because the first step is to plan the repairs, and that will cost $94 million. 

It's not just fires that these old Los Angeles class boats have to worry about. Three years ago a 25mm (one inch) hairline crack was found on the pressure hull of the (then) 14 year old USS Toledo. The crack was in the metal plate, not a weld, which was replaced. Above the crack there was a 53 cm (21 inch) hairline crack in the outer (non-pressurized) hull, which was under the sail. The USS Toledo had just undergone a three year refit, costing $179 million when these cracks were discovered. The sub was sent to a nearby (to New London, Connecticut) shipyard for repairs. At first it was thought some of these cracks were related to a recent scandal where shipyard workers failed to check for substandard welds but that was not the case with the Toledo.

Such a crack in the pressure hull is a serious problem because it makes it more likely that the pressure hull would fail and flood the boat, at less than the "test depth" (about two thirds the "design depth," which is the maximum depth the sub can operate at). Going a little deeper gets you to the collapse (or "crush") depth, at which the pressure hull is crushed and implodes. The deepest diving U.S. subs, the Seawolf class, are believed to have a test depth of 490 meters (1,600 feet) and a collapse depth of 730 meters (2,400 feet). During World War II collapse depths were never more than 320 meters (a thousand feet). Since then, larger boats, built of stronger metals, have greatly increased the depth subs can operate at. But that only works if the crew knows the limits of their boats, and cracks in the pressure hull reduce those limits.

Both the Miami and the Toledo were among the latest "improved Los Angeles" boats. If the Miami were retired, a much older (in terms of technology) boat would have to delay retirement and fill in. Upgrading one of these older boats would also be expensive. If the repairs for the Miami do indeed cost less than half a billion, then it's worth keeping the Miami in service.

The navy is putting most of its cash into building new Virginia class boats to replace the 42 (of 62) remaining Los Angeles subs. The most recent of Los Angeles boats entered service in 1996, and will be gone by the end of the next decade. Nine Virginias are in service and another 21 are planned. If the navy can scrounge up enough cash it can build two a year they can have all the Virginias in service before the Los Angeles class is gone. Otherwise, the SSN fleet will shrink because additional old Los Angeles subs will be retiring compared to new Virginia's entering service.


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