Sailors in US nuclear submarines usually experience less radiation than civilians ashore.
“The exposure to radiation from background sources – such as the sun and rocks underlying the soil – is normally higher than the radiation received on board,” points out Commander Ollie Lewis, US Navy captain of the nuclear-powered submarine USS San Juan.

“We pride ourselves on our safety record,” he adds.

“We have over 133-million nautical miles sailed by nuclear-powered warships, including aircraft carriers. There has never been a reactor accident. We are welcome in 150 different cities in 50 different countries and dependencies. This record is the result of the vision of Admiral [Hyam G] Rickover. We’ll always stick with conservative design, highly trained people, and in-depth procedures.” Admiral Rickover (1900–1986) developed the world’s first nuclear-propelled submarine, the USS Nautilus, and so was the father of the US Navy’s – and, by extension, all other navies’ – nuclear submarine forces.

“Nuclear power gives us endurance,” highlights Lewis. “We are limited only by the food that we can carry. We can operate submerged for months. We have no need to refuel. We can operate in a sustained and covert manner. A normal peacetime deployment for us – including visits to friendly ports – is six months. We left our home port, Groton, in Connecticut, on June 1 and we hope to be home by Christmas.”

The USS San Juan, which recently visited Naval Base Simon’s Town and exercised with one of the South African Navy’s new Type 209 conventional (diesel-electric) submarines, the SAS Queen Modjadji I, is a Los Angeles-class attack submarine – a US designation indicating that its primary function is to engage hostile ships. Under the abbreviation system developed by the US Navy but now universally used, it is an SSN and has the pennant number SSN-751, while the SAS Queen Modjadji I is an SSK, and ballistic missile submarines carrying nuclear-armed missiles are SSBNs.

Originally commissioned into service in 1988, the USS San Juan is now 21 years old and is about two-thirds of the way through its expected life. It is 110 m long, has a beam of 10 m and a draught (when surfaced) of about 9,75 m, and, when submerged, it displaces some 7 000 t. In comparison, the SAS Queen Modjadji I is 62 m long, has a beam of 7,6 m and a draught (when surfaced) of 5,5 m and displaces almost 1 600 t when submerged.

The American SSN has a crew of 140, while the South African SSK’s complement is 36.

Oddly, perhaps, Western SSNs have fewer torpedo tubes than SSKs – the USS San Juan has four, whereas the SAS Queen Modjadji I has eight (French SSNs also have four torpedo tubes, while British ones have five or six).

However, SSNs carry many more weapons. According to naval reference books, the USS San Juan can carry 26 weapons to launch through its torpedo tubes, which can be torpedoes, or a mix of torpedoes, Harpoon antiship missiles and/or Tomahawk conventionally armed long-range land-attack cruise missiles. In addition to these weapons, the SSN has 12 vertical launch tubes for Tomahawks, giving it a total of 38 weapons.

South Africa’s SSKs can each carry 14 weapons, currently torpedoes only (they can carry antiship missiles, but South Africa has not acquired any yet).

The USS San Juan is powered by a single Westinghouse submarine-specific S6G pressurised water reactor which powers two steam turbines which drive a single shaft and screw (propellor). “The reactor generates enough steam power for us to go faster than 25 knots,” says Lewis.

Reference books report a top speed for the USS San Juan and her sisters of 32 kt to 35 kt. According to the UK Royal Navy, an SSN can travel more than 500 miles in a day.