Detail from the official photograph of HMS Rushen Castle (IWM Negative No FL7294 - Crown Copyright) showing the location of some of her weapons. 

Reproduced here with the kind permission of the Imperial War Museum.  Please note: Imperial War Museum images may not be copied without the permission of the Imperial War Museum.

My thanks to Mark Walters of the Flower Class Corvette and WWII Royal Navy forums for "filling in the gaps" in my knowledge.

First you may notice the cages on either side of the 4" gun to the right of the photograph - these are rocket propelled flare launchers. They were mounted at a fixed angle and carried three rockets each side. The flare was often known as "Snowflake" and was used to illuminate U-boats on the surface so that the gun crews could target them.

To the left of the photograph, on a wing of the bridge, is an anti-aircraft cannon, a single 20mm Oerlikon (see close-up below).

The "Squid" * platform with a single "Squid" mortar (under covers - see close-up below) is also identified on the photograph, located immediately forward of the bridge. Castle class corvettes had only one Squid due to its weight and the storage needed for the ammunition. The later Loch class frigates carried two mortars. The first ship to carry a production "Squid" was a Castle class corvette, HMS Hadleigh Castle, in September 1943.

The following is Colin Warwick's explanation of the use and effectiveness of this weapon, as taken from his book, "Really Not Required".

"The new construction Castle class frigates possessed the latest high technology developments for A/S Warfare. HMS Rushen Castle's sonar or asdic equipment combined both a surface-range oscillator and a depth-recording asdic which was accurate, plus-minus 5 feet.

"The depth-charge armament consisted of a three-barrelled 'mortar' carrying three 250-pound 'aircraft bombs'. This weapon was located just abaft the fo'c's'le, below the ship's bridge, and could be trained automatically ten degrees on either side of the ship's centre line. The depth charge 'bombs' were fired automatically when the attacking ship was 500 feet from the U-boat target. The depth of the contact at the time of firing was set on the charges.

"When asdic contact with a submerged U-boat was obtained the ship was conned head-on to the target followed by the order 'Steer by asdic' **, whereupon the attacking escort ship was kept head-on to the asdic bearing shown on the recorder in the wheelhouse. At the same time the 'squid' cannon or mortar was being trained on the asdic bearing. The 'ping' of the asdic contact was relayed to a speaker on the bridge from the little radar and asdic operations room at the rear of the open bridge." (Click on attached file)

"The 'squid', as it had been named, was a most accurate and lethal anti-submarine weapon. It could be activated within a few minutes for a quick and most accurate depth-charge attack at up to 15 knots. Whereas in the past the depth of the U-boat was merely estimated, now the actual depth was being recorded on the fast sinking charges. No longer could a U-boat commander dive to extreme depths to distance his vessel from the attacking escort ship's formerly estimated depth settings.

"After some three and a half years ... it was luxury indeed to have all the required information supplied by accurate and instant high-technology equipment, manned by the most capable and efficient officers and ratings, enabling me to make the right decision."

Colin Warwick's delight with his new weapon seems at odds with a Wikipedia article *** on the internet which, in emphasising that Castle class corvettes were "seriously under-powered", states, "the fact that attacks with 'Squid' required a fairly low speed compared to depth charge attacks only made matters worse."

The excellent photographs below (© Copyright Eugene L Griessel - reproduced here with his kind permission) offer rare close-up views of a "Squid" (left) and a single 20mm Oerlikon, exhibits at the SA Naval Museum, Simon's Town in South Africa.

*   Wikipedia contributors (2006). Squid (weapon). Wikipedia, The Free Encyclopedia. Retrieved 11:13, February 26, 2006 from http://en.wikipedia.org/w/index.php?title=Squid_(weapon)&oldid=39324810.

**  The words 'Steer by asdic' have been inserted by me with reference to another passage in "Really Not Required" as I felt they may have been an accidental omission from the original text.

*** Wikipedia contributors (2006). Castle class corvette. Wikipedia, The Free Encyclopedia. Retrieved 11:18, February 26, 2006 from http://en.wikipedia.org/w/index.php?title=Castle_class_corvette&oldid=40013100.