ASDIC in HMCS SACKVILLE

Once of the benefits of having HMCS SACKVILLE in for refit is that we are able to access compartments that would normally be inaccessible. Two of those spaces are associated with the ship's original underwater sensor suite (originally knows as ASDIC, now better known as SONAR) as well as the former chain (or cable) locker, which I believe was retrofitted at some point to accommodate an underwater sensor of its own.

It should be noted that while much of the following has been contributed by others, more knowledgeable than I on ASDIC/SONAR, we are hoping to find someone who may have been familiar with the installations within SACKVILLE (or corvettes in general) either during the war or after during SACKVILLE's days as a loop layer and research vessel. In particular, my thanks to (in no particular order) Jerry Proc, Clive Kidd, Koji Kamori, and Norrie Millen for their observations and help in interpreting the fittings that remain in SACKVILLE.

In the section below, the ASDIC compartment is labelled as "NO. 1 STORE ROOM" just aft of the cable locker.

Viewed from the exterior of the hull, you can just see the through-hull penetrations from the ASDIC compartment on the left of the following image, with another through-hull penetration from the cable locker on the right.

All of these openings have been plated over to prevent leakage. Viewed from underneath, the ASDIC compartment penetrations can be seen clearly (aft is to the left, the bow is towards the right of this image):

And the opening from the cable locker:

ASDIC was originally developed during the First World War, but was still fairly primitive at the start of the Second World War. SACKVILLE was originally fitted with a Type 123 ASDIC, which was developed in the 1930s. From my writeup on the Haze Gray and Underway website:

"Due to the primitive electrical systems on the early corvettes, these ships had to rely on magnetic compasses, rather than more advanced and reliable gyro compasses. The reliance on magnetic compasses limited these ships to the older Type 123A sonar, as newer sonars required gyro compasses. The use of magnetic compasses alone was a limiting factor, as they were sensitive to the steel construction of the ships on which they were mounted, and tended to bounce around in heavy seas and when the corvettes were thrown about after dropping depth charges, which made it difficult to plot an accurate course.

These "primitive but reliable" sonar sets used an oscillator located under the hull which could be rotated through 360 degrees (by hand!), but was fixed at about 6 degrees below the horizontal. As a result, conditions under which a submarine could be located, and contact maintained, were limited. As the oscillator was fixed in elevation, a corvette was forced to lose contact with a targeted U-boat during the actual attack phase where the corvette passed over the U-boat to drop depth charges, and one tactic early in the war was for one corvette to stand off and hold the contact while another corvette went in for the attack. The development of the Hedgehog, and other "stand-off" weapons later in the war, also helped to overcome this shortcoming.

The improved 123D set came about merely by adding a second magnetic compass and bearing indicator on the bridge, and a loudspeaker system for the sonar operator to communicate directly with bridge personnel. The upgrade appears to have occurred sometime between 1942 and 1943 for some ships, but was never fully carried out in favour of other more improved sonar sets."

The underwater portion, or "hull outfit", of the Type 123 ASDIC unit looked very similar to the following diagram, which I have borrowed from Jerry Proc's excellent website, which he in turn borrowed from another website, and which probably originates from a book of some sort:

On the inside of the ship, only the top protrusion would be visible. The following photo is reproduced from page 102 of Thomas Lynch's book "Canada's Flowers", and shows the ASDIC compartment of HMCS ALBERNI in 1941. The photo is looking to forward and to port, with the forward bulkhead (common with the chain locker) to the right and the interior of the ship's hull in the background. The winch to the left was for raising and lowering the oscillator (transducer) unit. 

The shelf in the corner (middle of the photo, with the boxes on it) appears at the bottom of the ladder in this photo taken this past week inside of SACKVILLE's ASDIC compartment (this photo looks in the opposite direction, to aft and to starboard):

Just to the left of the orange ventilation hose are the two openings (one with a gate valve installed on it, the other with a blind flange installed). In addition, aft of the ASDIC openings, there are two cylinders (with covers) on either side of the ship's keel which we have not yet identified. One suggestion (probably the most likely) is that they were transducer pockets for an echo sounder. (Note: This suggestion has been confirmed by several people - the pots would have been filled with an oil to keep air out of the cylinders.) 

Generally, the Flower-class corvettes were later upgraded with the Type 127 ASDIC as a stepping stone to the later, more advanced, Type 144. Again, stolen from my writeup on the Hazegray site:

"Macpherson and Milner indicated that the Type 127D was an interim upgrade to early Flower class corvettes between the fitting of Type 123 and the later, much improved, Type 144 set. The Type 127D introduced motorized rotation of the oscillator, and the oscillator was stabilized to maintain a constant attitude regardless of the movement of the ship. The Type 127D also required a gyro compass, and required that the ships be rewired with a low power system. In addition, the Type 127D could be used in conjunction with the new Hedgehog ASW mortar, although without complete integration between the two."

Some corvettes would also have received the Type 144 ASDIC, which would have looked similar to the following diagram (borrowed from the Weapons and Warfare website).

A labelled version follows:

The interior of the Type 144 appeared as follows (courtesy of the Australian War Memorial website):

From my writeup on the Hazegray site: 

"An improved sonar set with a fixed gyro-stabilized oscillator that used a gyro compass for bearing indication. The Type 144 was fully integrated with the Hedgehog or Squid ASW mortars. The Type 144Q was a Type 144 sonar with a "Q" attachment, which was a second oscillator that trained with the main oscillator, but was elevated down further for maintaining contact with the target at close range (possibly around 400 yards).

See Jerry Proc's website (link below) for an excellent description of these sonars, as well as a diagram showing how the Type 144, 144Q, and 147F worked together.

According to Norrie Millen (retired Royal Navy):

"I think under ideal conditions a range of 2800 – 3000 yards was possible, all depending on sea state, temperature of water etc. Q and Q2 [attachments] were used for close range and the switch was made just before instant echoes [were] reached to ensure target was not lost. I do not remember switching to Q at 1200 yards. I had 144 on my 3rd ship (1961-63)."

SACKVILLE's forward boiler was damaged during the war, and not repaired. Because of this, SACKVILE was retasked as a training vessel, and then a loop layer. After the war, she was modified to become a research vessel. Because of this, it isn't immediately clear whether she received the Type 144 set. To complicate matters further, we don't know what sensors she received during her time as a research vessel, and how the original fittings were modified to accommodate those sensors. Presumably as part of her research work, her cable locker was also fitted to accommodate some sort of sensor - the following photo shows two (open-topped) cylinders (or pots) on either side of the keel that look similar to the covered cylinders in the ASDIC compartment, in addition to the gate valve fitted to the through-hull penetration (on the centreline running between the two pots, and towards the top left of the image).

This image only shows one of the two pots, but shows the gate valve on the through-hull penetration a bit better. 

In addition, the cable locker was fitted with a voice pipe, for purposes unknown. Another view of the cable locker, looking forward:

One of the two pad eyes still has the remains of a shackle attached to it - I'm guessing that the ends of the ship's two anchor chains might originally have been shackled to the pad eyes to prevent them from going overboard when dropping the anchor.

And if you're wondering - yes, that is the interior of the ship's hull plating on either side of the photo. When the ship is afloat, there is water on the other side of that steel plate. As a museum ship, SACKVILLE is ballasted down to compensate for a lack of fuel and ammunition, and all sorts of other kit that has been removed over the years. If you look closely on both the left and right of the photo, you can see the scum line left by ballast water, as this compartment would normally be full of water when she is afloat.

If anyone has comments or information that might be useful to add to this post, please leave it in a comment, and I will see what I can do to incorporate it.

HMCS IROQUOIS: Exterior Tour

To finish up the tour of IROQUOIS, I will walk through some of her exterior features and equipment. When the IROQUOIS class received the TRUMP refit in the 1990s, they were optimized for Air Warfare, but retained the Undersea Warfare capability originally fitted, and had limited Surface Warfare capability. Some of the photos here go back to the 1990s, and may have been taken on ATHABASKAN. My understanding of these systems is very basic, so my descriptions will not be very detailed. Which is probably just as well.

Undersea Warfare:

Designed as anti-submarine destroyers, IROQUOIS and her sisters were fitted with the latest in Canadian sonar equipment, originally the Computing Devices Canada (CDC) SQS-505 hull-mounted and variable depth sonars. These were later upgraded to the SQS-510 model. A number of years ago, I wrote an outline on RCN sonar systems here. 

SQS-510 Hull Outfit C3 sonar dome, removed for maintenance. The fairing itself is seen at bottom left, and is facing backwards.

Unlike the huge low-frequency bow-mounted sonar domes favoured by the US Navy and others, the RCN currently uses medium-frequency sonars in a smaller faired dome, situated just forward of the bridge. In previous classes, the sonar dome was originally designed to be retracted into the hull to reduce the ship's draft when entering port, but they were later fixed in the down position. I believe IROQUOIS was designed with the dome in a fixed position. This means that special care must be taken when dry docking these ships, to the extent that the graving dock at the Halifax Shipyard has wells cut into the bottom to accommodate the sonar dome and the propellers of these ships.

IROQUOIS also carried a second SQS-505/510 in a Variable Depth Sonar (VDS) system fitted at the stern.

SQS-510 towfish and launching gear. Note the faired cable that would lower the towfish to depth.

The VDS launching gear was installed in a cut-out in the transom. The operator worked behind the windows on the port side of the well, and the two ports on the starboard side are for the Nixie torpedo decoy.

The launching derrick would lift the towfish off its cradle, and pivot out over the stern to lower the towfish into the water. The towfish would be lowered to an appropriate depth via a faired cable, and would provide better detection abilities than the hull-mounted sonar as it would be not be affected by hull noise, and could be lowered below thermal layers that might mask the presence of a submarine.

Towfish being launched. Image courtesy of Corvus Publishing Group.

VDS was a Canadian Development in the 1950s, and was adopted by several other navies before being supplanted by towed array sonar systems such as the SQR-19 / CANTASS towed array sonar fitted to the HALIFAX class. The VDS was removed from the IROQUOIS class sometime in the first decade after 2000. 

VDS towfish cradle after removal of the VDS.

Once a submarine had been detected by sonar, Mk.46 lightweight torpedoes could be deployed against it from either the ship itself or a Sea King helicopter. 

Starboard Mk.32 triple torpedo launcher.

Unlike the fixed double Mk.32 launchers that fire at 45 degrees out the forward corners of the helicopter hangar on HALIFAX class frigates, the triple Mk.32 launcher on the destroyers was trainable and had to be directed out over the side. It is shown here in the stored position. Compressed air would be used to force the torpedo out of the tube and into the water, from where it would deploy its own motor and hunt for a target. 

Air droppable Mk.46 lightweight torpedo. A parachute is fitted in the cowling over the propeller nozzle.

The Mk.46 torpedo could also be carried by a Sea King helicopter, and air dropped with the help of a parachute that would detach when the torpedo hit the surface. These lightweight torpedoes are much smaller than the heavyweight ones carried by submarines.

Air Warfare:

Originally fitted for point-defence against aerial threats, the IROQUOIS class was refitted under TRUMP with area air defence systems that could extend an umbrella of protection to other ships operating in a task group, or to defend a convoy. First, all the radars were upgraded as part of that refit. (I have also written a summary of radars and fire control system used by the RCN over the years).

The main mast is bristling with sensors and other antennas.

Antennas for all of the primary air warfare sensors can be seen in the photo above. Looking from bottom to top, there is the port WM-25 Separate Target Illumination Radar (STIR), the LW-08 (AN/SPQ-502) long range air search radar, two navigation radars, and then the DA-08 (AN/SPQ 501) air/surface search radar antenna on the top of the main lattice mast. 

Port WM 25 STIR, with LW-08 in the background.

IROQUOIS carries two STIRs, port and starboard over the bridge. These would track and designate or "paint" targets for the ship's weapons systems, after being detected by the ship's other air defence radars. All the radars are gimbal-mounted to allow them to maintain a level disposition while at sea.

LW-08 long range air search radar

The LW-08 and DA-08 are the primary air defence radars, the former optimized for the long range detection of aerial targets, and the latter mounted higher on the main mast to provide better over-the-horizon aerial and surface detection. I believe the bar piggy-backed on top of each antenna dish is an Identification Friend or Foe (IFF) device. 

DA 08 air/surface search radar.

The primary air defence weapon is the Standard SM-2MR missile, deployed via a 29-cell Mk.41 vertical launch system (VLS). 

Mk.41 VLS.

Each cell of the 29-cell launcher can fit one SM-2 missile, or four RIM-162 Evolved Sea Sparrow Missiles (ESSM) in a quad-pack. Although the ESSM has now been added to the HALIFAX class ships in their Mk.48 VLS, I do not know if the IROQUOIS class has ever carried them. The launcher actually has room for 32 cells, but three cells are taken up by a strike-down crane (third row in, on the right of the photo above). This crane is apparently never used, and has been removed from later launchers in favour of three additional cells. In way of comparison, a USN BURKE class destroyer carries up to 3 of these launchers.

As an aside, the only vertical launched Sea Sparrow missiles that I am aware of ever being deployed from an IROQUOIS class ship was the 1981 testing of the Mk.48 VLS from HMCS HURON. I have seen a photo somewhere, as I recall showing two Mk.48 cells fixed to the side of the old Sea Sparrow launcher used by these ships pre-TRUMP.

Secondary air warfare defence is provided by both the OTO Melara 76mm gun, and the 20mm Phalanx Close-In Weapons System (CIWS). (Another version of this acronym that I have seen reads "Christ, It Won't Shoot"). 

Phalanx CIWS.

The Phalanx is a self-contained unit combining a 20mm gatling gun with a radar system, and is easily bolted onto ships that weren't necessarily designed to carry them. They are intended as a last ditch weapon to try and stop missiles ("leakers") missed by the primary missile system. The RCN retrofitted its Phalanx systems to the Block 1B standard, complete with the camera mounted on the side of the radome to help provide anti-surface capability.

IROQUOIS also carries four Plessey Shield flare and chaff launchers just aft of the bridge, and was also retrofitted with the Australian Nulka active missile decoy system.

Nulka launcher on the quarterdeck of ATHABASKAN in 2010.

Port Nulka launcher aft of the bridge of ATHABASKAN in 2010.

IROQUOIS can carry up to four Nulka launch cannisters, two port and starboard behind the bridge, and two side-by-side on the quarterdeck just aft of the helicopter deck. Nulka launches as a rocket from the cannister, but then can hover away from the ship and attempt to draw incoming missiles away from the ship. I was under the impression that the RCN did not buy enough units to fully equip all ships of the class, and would trade them off between the ships (on the East Coast at least).

Surface warfare:

Lacking dedicated anti-surface missiles like Harpoon (although I believe the SM-2 missile can be used against a surface target in a pinch), IROQUOIS relies primarily upon her 76mm gun and Phalanx CIWS (supplemented by .50 calibre machine guns for small surface craft). A summary of other gun systems used by the RCN over the years can be found here.

OTO Melara 76mm Super Rapid gun.

The Super Rapid version of the gun can fire 120 rounds per minute, and is improved over previous mountings to help counter anti-ship missiles as well as surface targets. The gun has a dedicated fire control system in the Lightweight Radar/Optronic Director (LIROD).

LIROD.

The LIROD is mounted between, and slightly forward of, the two STIRs.

This concludes, at least for now, my photo tours of IROQUOIS. I finish writing this just in time on April 25, 2015, less than one week before IROQUOIS pays off on May 1, after which 43 years of being "Relentless in Chase" will come to an end.