Fixing a flat tire without a spare can be a challenge on lonely country roads. Do you call a tow truck, or do you hike to the nearest farmhouse?
But if you're in a nuclear submarine that gets a ''flat,'' hiking is not one of your options.
However, there is a tow truck for the US Navy's nuclear submarines. It's called a Deep Submergence Rescue Vehicle (DSRV). The Navy has two of them, DSRV Mystic and DSRV Avalon. Each can dive as deep as 6,500 feet to repair submarines or rescue crew members should repairs not be possible.
DSRVs are ready to go anywhere in the world within four hours. Should an emergency occur, they can be loaded on an 18-wheel tractor-trailer and driven onto an Air Force C-5A cargo plane.
When the plane lands at the submarine base nearest the stricken sub, the DSRV is loaded piggyback onto a ''mother'' submarine to be ferried to the repair site. The DSRV will then disengage itself from the mother sub, and traveling at two to four knots, meet up with the disabled submarine.
The DSRV then attaches itself to an emergency hatch on the rear of the immobilized sub. Eighteen crewmen at a time can be taken out of the stranded sub and transferred to the mother sub by the DSRV. This is repeated until all the crew is removed.
One wag summarized the operation: ''Cramped quarters on a sub are a given. On a DSRV the only thing that separates the men from being sardines is they know that when they get out of the can they are going to be alive.''
Another role of the DSRV is to retrieve nuclear warheads or secret codes on board a damaged submarine that will not be able to surface.
Since the Mystic and the Avalon were launched in 1970 and 1971 respectively, neither has had to make a rescue. ''That's just fine with the Navy,'' says Chief Warrant Officer Max Alexander assigned to the DSRV base in San Diego. ''And we hope we never have to. But it's a real morale booster to the men to know we have the capability to come get them.''
When the nuclear submarine USS Thresher went down in 1963 with all hands aboard, the Navy began research on a rescue vessel. The loss of a second fully manned nuclear sub, the USS Scorpion in 1967, speeded DSRV development.
The personnel assigned to a DSRV are technically oriented. ''They usually have three to five years' minimum regular submarine experience,'' says Lt. Richard T. Luke, skipper of the Avalon.
Duty on the DSRVs is so popular that about three applicants try for each opening. ''In fact,'' Chief Alexander says, ''they (DSRVs) help us keep career submariners who may otherwise leave the service for the scientific research community.''
DSRVs are on highest alert during the first four hours at sea for any sub that has just had a major overhaul. During that time all the systems on a submarine, as well as the stress tolerances of its hull, are being checked and often pushed to their limits.
''This is when we are most ready to go,'' says Lieutenant Luke. ''Even if a sub goes down in waters deep enough to crunch its hull, we still go down and find it.''