July 27, 2012:
On July 17th one of Canada's Upholder class submarines (HMCS Victoria) was the first of its class to fire a torpedo at a ship and sink it. Victoria used a Mk 48 torpedo to sink a 16,000 ton former U.S. Navy supply ship (USNS Concord) in a SINKEX (sinking exercise). The Concord took 18 minutes to sink.
This SINKEX occurred during this year's RIMPAC (Rim of the Pacific) exercises. Since 1971, RIMPAC has served as a training exercise which brings together military forces from American allies bordering the Pacific (especially Australia, Japan, Canada, and South Korea, plus the occasional European ally that has ships in the Pacific). This sort of thing is essential to train crews for combat and check that allies are capable to coordinate operations under wartime conditions.
RIMPAC exercises are particularly valuable for their anti-submarine warfare training, since it's one of the rare opportunities the U.S. Navy has to practice against some of the latest diesel-electric submarines that are well-manned. Australia, South Korea, and Japan usually send their subs to sink (in a realistic but simulated fashion) some of the most capable surface ships in the world and simultaneously avoid some world-class anti-submarine forces. The subs often win.
For most of the last century the U.S. Navy has conducted SINKEX training. In the last two decades about two ships a year are sunk, most off the coast of California or Hawaii. SINKEX enables the navy to test new theories on how vulnerable, or invulnerable, modern warships are and how effective new, or current, weapons are. With the advent of smaller, cheaper, and more reliable sensors and broadcasting gear it's possible to get a lot more data out of a SINKEX target and monitor the damaged ship as it is hit until it goes under. This leads to changes in ship design and damage control techniques.