The USS Stewart, Seawolf Park, Galveston Texas

The Stewart (DE-239) was a DE (Destroyer Escort) and consequently a submarine killer.   Destroyer Escorts were used to patrol for submarines and to escort convoys across the Atlantic ocean.   Once a DE encountered a submarine it proceeded to use it arsenal of weapons to destroy the sub.   Please see this youtube video about WW-II submarines

Destroyers had several anti-submarine weapons guns for a sub on the surface and depth charges and hedgehogs for a submerged sub.    

Guns
The guns on a destroyer ranged from 20mm, to 40mm Bofors, and to 5" cannon.   These guns were primarily used for submarines on the surface and mounted on the upper decks.  

Depth Charges
WWI weapons for destroying submerged submarines.   The WWI depth charges were little more than barrels with a pressure trigger that detonated at a specific depth.   These barrels tubmled as the sank causing them to be slow and drift off target.   Later depth charges (mark IX and such) were teardrop shaped with fins which caused them to sink straight down and rotate, keeping them in a vertical descent.   Depth charges were initially rolled off the tail of the destroyer then later launched on each side by K guns as the destroyer passed the submerged sub.   The depth charges slowly sank to a specific depth where they exploded creating a powerful hydrostatic shock wave that could damage a sub if it were near the explosion.   One problem with depth charges were the sub hears the depth charges enter the water and can dive deeper or turn to avoid the worst of the explosions.   Another problem with depth charges was all the chaos created by the hydrostatic shock waves from depth charge explosions masked the sub from the destroyer's sonar for about 15 minutes.   If a destroyer managed to suffuciently damage a submerged sub to cause it to surface, the destroyer's guns were brought into action to sink the sub.   Please see the Wikipedia page on depth charges.   The kill ratio for depth charges was about 5-7% during WWII.

Hedgehogs
The Hedgehog was an interesting anti-submarine weapon, it was developed by the Brittish for U boats, then adopted by the US Navy late in the war.   The hedgehog's spigot mortars had contact triggers and only exploded on direct contact with the sub's hull, thus reducing the amount of explosive required to breach the hull and the amount of hydrostatic turbulence that could mask the sub.   The hedgehog fired it's Spigot Mortars in a spread pattern ahead of the destoyer, thus the sub could not easily avoid them.   Since the hedgehog only exploded when it struck the sub and it was fired in front of the destroyer the destoryer could continually track the sub by sonar.   Please see the wikipedia page on Hedgehog.   The kill ratio for Hedgehog was about 20-25% during WWII, an considerable improvement over depth charges.  
YouTube video of Hedgehog demo and good explanation about the hedgehog.
I here is a link to a modern system based on the Hedgehog's concept.      

The Stewart's screws and two deck guns.

USS Stewart port side.

Betty eyeing the guns on the Stewart.

A 3" gun and a 40 mm. bofors on the forward deck.

You can see a few Bofors mounts on the after end of the Stewart.

Betty going into an internal passage from the galley.   You can see steam pots on the left and a stove on the right.

Better look at the steam pots.

Mess.

Steam table in the mess area.

Ice cream machine and storage in the mess.

Crew's bunks, stuck in evey nook and cranny.

Bunk room.

More bunks.

Betty going forward on the Stewart's port side, note the Cavalla to the left.

Betty passing the Hedgehog.   Another HedgeHog Pic, and a Hedgehog at Fredericksburg

Anchor chains on the bow.

Looking back at the bridge.

Beside a 3" gun looking back at the hedgehog.

I'm not sure what caliber this deck gun was.

Another look at the hedgehog.   I understand the tube at the base of the Spigot Mortar contained propellant and fit over a rod (you can see one front right).   Notice the different angles of each mortar, it sets a pattern that a sub can't avoid.

From an upper deck, looking back at the stack and some Bofers mounts.

I think this was CIC.

Looking into the bridge.   You can see the helm and the 3 knobs on the engine telegraph (old term).

One of the large search lights on the upper deck for scanning the sea at night.

Looking down at the Cavalla.

Looking forward from above the bridge.

A couple of 20mm machine gun emplacements, one being refurbished.

A dual Bofers mount.

Another daul Bofers mount.

A quad Bofers mount.

A dual Bofers with a 20mm on the left.

Betty under a gun mount on the starboard side.

Part of the head.

Another part of the head.   I assume there was something under the seats.

Another shot of the head.

Depth charge palque.

Dept charge racks on the fan tail.   The depth charges were loaded onto these racks then allowed to roll off the afte end of the ship, at intervals, as the destroyer passed a submerged sub.

K gun plaque.

K guns on the port after deck along with some old barrel shaped depth charges.   The fired depth charges to each side of the ship as it passed a submerged sub.

More modern K gun with a teardrop shaped (Mark IX) depth charge at Nimitz Museum.

Another K gun with modern (Mark IX) depth charge at Nimitz.

Hedgehog at Nimitz Musuem.