ROYAL NAVY HARBOUR DEFENCES - MANZA BAY, TANZANIA

Manza Bay - north heads	Kronborg - on fire in Manza Bay	Manza - Command Post

Manza Bay is located on the coast of Tanzania, some 16 km north of the town of Tanga. During World War I a German vessel called the Kronborg (actually the captured British vessel Rubens), on a mission to resupply the besieged SMS Königsberg, was sunk by the British ship HMS Hyacinth.  During World War II,  Tanzania's northern neighbour, the British colony of Kenya, was a temporary base of the British Eastern Fleet from early 1942 until the Japanese naval threat to Colombo and Ceylon had been removed. This is a story of the indicator loop defences at Manza Bay. Further information about Kenya can be found on the Mombasa Forts webpage.

If you worked there or have any feedback please email me: Dr Richard Walding   Research Fellow - School of Science Griffith University Brisbane, Australia Email: waldingr49@yahoo.com.au

My thanks to Hans-Martin Sommer M.A., former Marine Archaeologist, Fort Jesus Museum, Mombasa, Kenya for his assistance in providing photos and some text for this webpage. Email: <sudanhansm@yahoo.de>. Hans-Martin has started a project called: "Defense of Mombasa, 1485- 1945". The range of objects begins from early Turkish and Portuguese fortifications and ends with many British bunkers, tunnels and other fortifications and harbour defences. Hans-Martin has previously worked in Germany, Spain, UK and Poland and has published widely. He is a member of the British Institute in East Africa and the Institutum Canarium. He is photographed here in 2006 at a bunker at Kipevu (Port Kilindini) Mombasa. His evidence for indicator loop defences at Manza Bay adds to the rich military history of Kenya and Tanzania. Thanks to Steve & Cathy Attwell (Tanga/Arusha, TZ), the owners of the nearby Fish Eagle Point for accommodation and transport, Robert Elder (Geita,TZ) for providing information.

Indicator Loops - an overview (YouTube, 70 minutes)

MANZA BAY HISTORY

World War One. From the beginning of WW1 in August 1914 until June 1916, all the coast towns of Eastern Africa — Tanga, Pangani, Sadani, Bagamoyo, and Dar-es-Salaam — remained in the enemy's hands, and, though the blockade of the coast carried out by the Royal Navy prevented these seaport towns from receiving any supplies of food or munitions, there was still a danger that German troops in them might strike westwards, and make flank attacks upon the allied forces working southwards. In these circum-stances, the British decided that the towns on the coast must be wrested from their German enemy, and the Royal Navy was called upon to assist in the task. Manza Bay was the first of the German East Africa ports to fall to the British in WW1. For the British, in home waters there was always the possibility of bumping a mine, or being hit by a torpedo, but off the coast of East Africa there were none to be found. On 7th June 1916 British military forces, which had landed at Manza Bay under cover of the guns of the Talbot and Severn, occupied Tanga, after encountering but slight opposition from enemy patrols. For the British, in home waters there is always the possibility of bumping a mine, or being hit by a torpedo, but off the coast of East Africa there were none to be found. The place had been the scene of a bad disaster in the early stages of the campaign, and consequently its occupation was not without dramatic interest. The German defenders made no real attempt to defend the town, but cleared out of it before our troops had time to reach it. The Vengeance (flagship) sent her band ashore to play the National Anthem when the Union Jack was hoisted over the Governor's house, and, except for the attention of a few persistent snipers, all was as calm. So the first of the seaport towns of German East Africa fell into British hands.

On 27th July 1939, the British Admiralty finalised its minelaying program for ports at home and abroad for the early stages of the war should it occur. The Admiralty policy was that minefields should only be laid at the outbreak of hostilities and not before as the cost of maintaining the mines and the minefield was prohibitively expensive. Minefields were planned for Hong Kong, Singapore, Alexandria, Malta, Tynemouth and Cromarty Firth. Upon outbreak of the war with Germany in September (1939) the minelaying program began in earnest.

The following is a description of the construction of fortification by the Royal Engineers by the officer in charge. The Indicator Loop cables were installed, connected and operated by the Royal Navy. The loop control hut and associated buildings (accommodation, power huts) would have been constructed by local labour. Reproduced in The Royal Engineers Journal, Vol 108, No. 2, August 1994, pp 201-208.

2. CONTROLLED MINEFIELD AT MANZA BAY
It wasn't until 1943 that the minelaying at Manza began. The main consideration by the Royal Navy was to defend Manza Bay against midget submarine and human torpedo attack. The initial idea in February 1943 was to use Antisubmarine boom nets, indicator nets (nets with carbide lamps that lit up if disturbed by a ship) and Harbour Defence Motor Launches (HDML Patrol Craft) as a general measure as well as a  controlled minefield against midget submarines.

The two Controlled Mining huts on Manza headland	Mavemaveli Rocks as seen between the two CM huts.

 

As defence against human torpedoes the Royal Navy planned to used three Indicator Loops (3-legged type) for detection and two Harbour Defence Asdics as a backup. It was soon decided to abandon the defences against human torpedoes as it was felt that capital ships were not in harbour long enough and to minimise the huge costs involved. Ultimately, the Navy decided to go for a double Controlled Minefield with the associated mine loops and guard loops. The guard loops at Manza Bay required 10.5 km of 18-core cable and the mine loop a further 2.9 km of cable. The loops also needed 7.2 km of tail cable. The mine cables themselves required about 2.9 km of cable. Personnel would have been trained at the Controlled Mining School at HMS Vernon (Portsmouth, England).   The document to the right is the cover page from the correspondence about the Manza Bay controlled mining taken from files in The National Archives, London. Click to see an enlargement.

Click to enlarge

Each of the two mine loops was about 700 yds long by 25 yds wide with four buoyant mines moored in the centre and attached to a firing cable. There was a 160 yd overlap between loops. There were three guard loops of varying lengths: A = 3000 yds, B = 4600 yds, C = 2850 yds and all were 25 yds wide, and overlapping slightly. These were positioned about 3000 yds on the seaward side of the minefield. Tail cables (4 core, as shown later) ran from each of the five loops to the shore and thence underground to the naval mine watch station. Guard Loop C was watched from a control station on the southern shore. The associated amplifier was the new Photovoltaic Amplifier Mark 1 (PVA).  In 1945 - at war's end - the Royal Navy may have exploded the mines if attempts to recover mines and sinkers was unsuccessful because of lack of power in the mine recovery winches; alternative they would have been recovered and destroyed. In other RN controlled minefields throughout the world the mines were also generally detonated and sometimes attempts at recovering the cables were made. In some countries only 50% of the cables were lifted as they were more likely to be covered in mud, sand or coral and after five years in the salty water the condition was usually poor. The layout of the minefield is shown below.

Map of Manza Bay with  locations of naval defences	Mavemaveli Rocks from the Mine Station window.

3. OPERATION OF The Extended Defence Officer's POST & Mine watching STATION. 
The Extended Defence Officer (XDO or EXDO) was the naval officer responsible for all naval activity in a given area. He had the responsibility for the minefield, boom nets, indicator nets and signals and was the liaison between the RN and army at north head. If the XDO's visual sightings and communication with the army revealed the likely presence of an enemy U-Boat, the XDO would give orders to the mine watch officer on duty. The orders and firing sequence were the same throughout all CM stations around the world. The men in the Mine Control Hut had to perform daily and weekly tests on the equipment to make sure it was in good working order and had to record perturbations ("perts" - the swings of the galvanometer spot due to the tides) every 5 minutes to the hour. These had to be recorded in the log book. At the end of each watch, the Handbook of Controlled Mining Confidential Book (CB) had to be mustered and had to be locked in a CB chest and then placed in a locked cupboard. The guard loops were 1000 yds to the seaward side of the mine loop so that if a submarine entered the bay it would cross the guard loop first and alert the CM operators. If a swing was detected on the guard loop, the operator would close the control switch to start the 300V generator and then ring one long bell to the power hut. The operator would then advise the XDO  "Mines to Active" and would say the letter of the guard loop (A, B or C) giving the swing. He would then check to see if the correct voltage was showing on the voltmeter. Then they had to wait. If a swing was detected on the mine loop after a swing on a guard loop it meant that a submarine had passed over the loops. The operator would then report to the XDO "Mines to Active" again, shift the selector switch to the number of the mine loop involved and fire the mines as the galvanometer spot crossed it's zero after it's first displacement. He would then say to the XDO "Mines to Active, mine number XX fired". After 5 seconds, the firing release lever would be released and the selector switch replaced. If there was just a swing on the guard loop they took no chances. The operator would fire anyway. After a firing took place, the fuses in the mine cable would be replaced. Of course, if a boat was sweeping for mines in the area, they should have told the XDO of the fact. Two other web pages showing the arrangements at other controlled mine stations are: Cromarty Scotland and Shellness in Kent, England.

4. CABLE TYPES
TAIL CABLE: Although no cable has yet being found at Manza Bay, the type of cable used by the Royal Navy was fairly standardized by 1943. The following describes the mining 'tail' cable. The longitudinal view (below) shows that the cable consists of four cores of 7 strands of 0.029" tinned copper wire laid up with a central square of white rubber and enclosed in a single layer of india rubber wrapped in a layer of waterproof tape. This is then covered with 28 galvanised steel armour wires (each 2.8 mm diameter). Then there is a braiding of two layers of dressed hemp yarn wound in opposite directions wrapped over hot pitch and resin, and finally a preservative coating. Final diameter 28 mm. The loop cable is not shown as none has been recovered from Cromarty. A 4-core able was typical up to 1939 but then the Adm. Patt. 660 (7-core) cable became standard. Pictures of this cable and the Patt. 7048 are on my Cablemakers website.

Cross-sectional view of RN Adm Patt 660 Controlled Mining 'Tail' Cable (sample from Moreton Bay, Australia, laid 1943). The outer dressing of hemp yarn has perished.	The  jute binding is as good as new after 70 years. The galvanised wire on the bottom is used to secure the cables to the wall. The rubber has surface cracks but is still waterproof.

LOOP CABLE: Cables used for controlled mining were Admiralty Pattern 660,  Pattern 7048 and Pattern 9610. Details of the cable types can be found on my Cablemakers website. It is interesting to compare this XDO Post with that of the Royal Navy's Cromarty (Scotland) Mine Watch Station.

5. THE MINES
The "L" Mark 2 mine units were the most common being used at that time. They consisted of two 40" diameter mild steel hemispherical pressings 3/16" thick joined with 1/4" thick bolts. The charge was 500 lb of amatol with an electric detonator (No. 28, Mark 2) inserted into a 1 lb charge of primer. The complete mine and charge weighed 3151 lb (1430 kg) and could disable a submarine within a radius of 40 feet. They had a positive buoyancy of 468 lb meaning they would float. To keep them moored, a sinker ("L" Mark 2) consisting of a cast iron base with a drum in the centre housing a cable that could moor mines in water up to 25 fathoms deep. 

Colour photos of Manza Controlled Mining Station taken February 2009. Photos copyright, Hans-Martin Sommer.

 

The mine control huts	Underground generator bunker

 

Channels leading from control hut	Channel - possibly for mine loop cable

 

Concrete slab - north head, Manza Bay	Gun Emplacement at Manza - North Head

 

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Fish Eagle Point - ocean resort
We have appreciated the help of Steve and Cathy Atwell in hosting expeditions to locate, photograph and map the Manza fortifications. Steve brought these to our attention in early 2009 and has facilitated the investigation. Steve and Cathy run the ocean resort on Mkadini Beach at Fish Eagle Point, Tanga, Tanzania, Africa. This uniquely beautiful ocean resort was opened for business late 2008. It is just north of the historic City of Tanga and is Northern Tanzania's first coastal resort. For more information go to their website Fish Eagle Point.

Fish Eagle Point - accommodation	Water sports - Fish Eagle Point

For more information about shipwrecks in Tanzania and Kenya see Shipwrecks and Salvage on the East African Coast 1499 - 2004 by Kevin Patience. Click the link to see a flyer in MS Word format. Using records in Australia, Germany, Kenya, Tanzania, Zanzibar and the U.K. as well as the library’s of Lloyds Register of Shipping, the Guildhall and the National Archives in London together with the Hydrographic Office records at Taunton, the author has discovered the stories of over 200 merchant and naval ships that came to grief. The publication covers most of the known casualties that were wrecked or salvaged along the coast from the Kenya / Somali border to the Tanzania / Mozambique border, a distance of 1,400 miles. The inland lakes including Tanganyika and Victoria also had their fair share of casualties and these are included, as are all the tugs from 1896 to date since many played a part in the salvage operations. The author spent over twenty-five years in the diving and salvage business in the Middle East and East Africa and was involved in some of the operations described in the book. He dived on and identified many of the other wrecks mentioned, and is indebted to people from all walks of life, who kindly opened their diaries and photo albums to find references and illustrations to some of the more obscure ship’s tales and all are acknowledged. 276 pages, H/Back, over 300 illustrations and three maps and weighs 800 gms. £15 posted to UK and £25 to other destinations by airmail. Available from the author - 257 Sandbanks Road, Poole, BH14 8EY saburi@hotmail.com

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