.50 cal. and 20mm guns can disable destroyers

... and 5 inch guns can sink them

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On June 7th, the U.S. Navy held another "Sink-Ex" (Sinking Exercise) some 450 kilometers off North Carolina. A Sink-Ex uses decommissioned navy ships for target practice, or, as in this case, to test new tactics. What the navy wanted to examine was the ability of current naval guns (from .50 caliber machine-gun to 5 inch cannon) to disable ships without sinking them.

Updated links:
Photos of the sinking of the Stump
The Stump in its better days
Another article re. the exercise
Wikipedia entry for the Stump

Conclusions: Well-aimed .50 caliber and 20mm gunfire can disable a ship.  5-inch gunfire aimed at the waterline can sink it. But, it takes some time. Missiles are not really needed (but would be quicker, when it is shooting back at you).

Nicholas @ MurdocOnline addresses the question of armor for ships, and gives some history.

see full size image in continuation

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The subjects of the Sink-Ex were two decommissioned Spruance-class destroyers (Comte de Grasse and Stump). These 7,800 ton ships, two of the largest destroyers ever built, were to be first subjected to gunfire, then Harpoon and Maverick missiles from air force B-52 and B-1B bombers overhead. The missiles did not get used, because the hail of gunfire sank the two ships within 90 minutes.

With cameras and sensors recording the damage, a variety of guns were turned loose on the ships, to see what kind of damage could be inflicted, how quickly and how accurately. Most of the results are classified, but it did appear that the .50 caliber and 20mm machine-gun were very accurate and effective, and capable of quickly disabling a ship without sinking it. Also tested were 40mm automatic grenade launchers.

The two ships were quickly sent to the bottom (12,000 feet below) with 5 inch gun fire directed at the waterline of the two 28 year old ships.

(According to one article, the Stump was decommissioned after corrosion was found behind piping insulation.)

The Coast Guard uses .50 cals to disable drug-smuggling cigarette boats, if necessary.