Planning a IJN strike against the Sembawang Naval Base

Had Britain arrived at the means to place a sizable fleet at the Sembawang Naval Base by autumn 1940, several months after the US Pacific Fleet completed its move to Pearl Harbour, could the IJN have planned for simultaneous preemptive strikes against both bases in Dec 1941? Of course we'd need to arrive at the means for the RN to have ships superfluous to Home and MTO needs to send a fleet, while not so changing the global balance of power to preclude any Japanese move into SEA, such as Italy joining the allies, or such. That aside, could the IJN hit Sembawang and Pearl at the same time? Presumably the Kido Butai goes to Pearl as historical, while the IJNAS' 11th Air Fleet and its G3M and G4M bombers would move on Singapore. With its narrow berths, the Singapore base looks like a tricky target for torpedo bombers. Did the IJNAS have any land based dive bombers? Of course some could be pulled from the fleet.

Just how much reserve strength did Japan have to provide adequate numbers to attack Sembawang?

The attack on Pearl was part of a much larger 8 December coordinated attack that included the Philippines, Guam, Hong Kong, Singapore, Malaya and 8 key objectives in Thailand.
All this while maintaining fronts in China.

How much strength would the Japanese Navy and/or Army would need in order to make the attack successful?

Admiral Beez said:

Had Britain arrived at the means to place a sizable fleet at the Sembawang Naval Base by autumn 1940, several months after the US Pacific Fleet completed its move to Pearl Harbour, could the IJN have planned for simultaneous preemptive strikes against both bases in Dec 1941? Of course we'd need to arrive at the means for the RN to have ships superfluous to Home and MTO needs to send a fleet, while not so changing the global balance of power to preclude any Japanese move into SEA, such as Italy joining the allies, or such. That aside, could the IJN hit Sembawang and Pearl at the same time? Presumably the Kido Butai goes to Pearl as historical, while the IJNAS' 11th Air Fleet and its G3M and G4M bombers would move on Singapore. With its narrow berths, the Singapore base looks like a tricky target for torpedo bombers. Did the IJNAS have any land based dive bombers? Of course some could be pulled from the fleet.

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As has been discussed before on other threads in the past these photo repesent only a small part of the naval facilities at Singapore in 1941. Here is a map of the whole base but there were other facilities, like tank farms, elsewhere on the Island. The majority of the fleet would have been anchored out in the Straits of Johore between Singapore Island and the Malayan Peninsula, all the way from the Causeway to the openings to the sea around Changi as the situation dictated.



Think of ships at Scapa Flow rather than Portsmouth or Devonport. Here is Scapa in April / May 1942 with US ships present having joined the Home Fleet.


Eastern access to the Straits of Johore for non-naval traffic was terminated with effect from 3 March 1941 by extention of the minefields. There were also Indicator Loops to detect any subs trying to sneak past the gun batteries placed there.

Distance from Saigon to Singapore is about 600 nautical miles. The question is whether the G3M & G4M aircraft could carry torpedoes all the way from the Saigon area to Singapore or the 800kg armour piercing bombs the Kates used at PH on Battleship Row to sink Arizona. Can't think of an IJNAF or IJAAF dive bomber with that range.

The G3M of the Mihoro Kokutai IJNAF bombed Singapore from Saigon on 8 Dec 1941 at 0400 with bombs landing around Keppel Harbour on the south side of the island, the naval base and the Seletar & Tengah airfields. Due to weather only 17 of 31 were able to bomb successfully, the rest turning back. Another raid by 34 aircraft of the Genzan Kokutai turned back entirely. These raids were detecte on radar but Singapore town was still lit up like a Christmas tree making bombing much easier. But I don't have details of the bomb loads these aircraft were carrying.

GrauGeist said:

Just how much reserve strength did Japan have to provide adequate numbers to attack Sembawang? The attack on Pearl was part of a much larger 8 December coordinated attack that included the Philippines, Guam, Hong Kong, Singapore, Malaya and 8 key objectives in Thailand. All this while maintaining fronts in China.

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AIUI, the air attack on the Philippines was carried out by the Imperial Japanese Army Air Force (IJAAF) rather than the IJNAS. As for the G3M and G4Ms of the IJNAS, I assume that those that attacked Force Z would instead attack the fleet at Sembawang. This of course assumes that the RN fleet has not left the base, but is moored like the PacFleet at Pearl.

Japan employed both Army and Navy to the 8 December attacks

In Thailand, it was a joint IJN and IJA operation.
Malaya was IJA while Hong Kong was a joint Army/Navy effort as was Singapore.

The initial 8 December attack on the Philippines was also a joint effort by the IJN and IJA, with Army air elements supporting the invasion and the Navy conducting bombing raids against Clark Field, which saw G3Ms and G4Ms escorted by A6Ms.

Guam and Wake islands were purely IJN.

GrauGeist said:

The initial 8 December attack on the Philippines was also a joint effort by the IJN and IJA, with Army air elements supporting the invasion and the Navy conducting bombing raids against Clark Field, which saw G3Ms and G4Ms escorted by A6Ms.

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I would expect this, as all three are all IJNAS aircraft. It would be more interesting to see Ki-43 Oscars escorting a force of Bettys. Did they even have compatible radios and codes?

Admiral Beez said:

I would expect this, as all three are all IJNAS aircraft. It would be more interesting to see Ki-43 Oscars escorting a force of Bettys. Did they even have compatible radios and codes?

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As far as compatible radio codes is concerned, I don't know - I would think they got on the same page prior to the operation. The radios would have been able to switch to whichever frequency was the primary designated for that particular operation.

In regards to the earlier mentioned IJN bombers at Clark Field, this was one of their few attack roles on the 8th, as the Army was taking the lead in striking Allied targets with types like the KI-21, flying in from bases in Formosa.
I am not sure if these Army bombers were escorted or not, but I do know of several instances were inter-service cooperation saw Navy bombers escorted by Army fighters (and vice-versa) n the Solomons and in the attack on Calcutta, KI-43s and A6Ms escorted Army KI-21s.

As for the IJN carriers that didn't go to PH;-

Ryujo - 12xA5M4 Claude (+ 4 spares) and 12xB5N1 + 2xB5N2 Kate (+4 spares) deployed to Palau to support landing at Davao in southern Philippines on 8 Dec (invasion convoy left Palau on 6 Dec).

Hosho - 11xA5M4 Claude and 8xB4Y1 Jean biplane TB.
Zuiho - 16xA5M Claude and 12xB5N Kate
Both attached to IJN Main Body of battleships & cruisers etc that sortied as cover for Nagumo's carriers returning from PH just in case the USN had managed to organise some retaliation.

Note lack of dive bombers and most of the Kates being the earlier B5N1 model.

Taiyo - escort carrier. Ferried A5M fighter aircraft to Palau unloading 6 Dec. Then returned to Japan arriving 12 Dec.

Shoho - only completed carrier conversion on 30 Nov 1941.

Another thing to bear in mind. By the time the Japanese attacked Malaya British forces were aware of the possibility of attack since 6 Dec Singapore time (5 Dec on the other side of the Date Line). As a result PoW and Repulse were able to fire on those first attacking G3M.

Now increase the fleet size and add it to the shore AA defences and the attackers can expect a hot reception.

This would not be like PH at 0800 on 7 Dec.

We should never underestimate the ability of Japanese war planners to overcomplicate any situation, and I believe we can agree that Japanese resources were pretty much maxed out to achieve their historical objectives in December 1941. How deep was the anchorage at the Sembawang Naval Base? Would the specially modified shallow water Type 91 torpedoes be needed? Would the special armor piercing Type 99 no. 80 Mark 5 bombs be needed to engage BBs? These could not be carried by any Japanese dive bomber at the time, but could their land based bombers carry it without modification? If either of these two specially modified weapons were needed to successfully attack the RN at Sembawang, there's a problem. As it was, both of these special weapons were not perfected, produced in limited quantities, nor were the Kido Butai sufficiently trained on how to employ them until just prior to their departure in late November 1941. Adding Sembawang to the target list, if the special weapons and employment tactics were needed there, would probably negatively impact the Pearl Harbor operation.

EwenS said:

Another thing to bear in mind. By the time the Japanese attacked Malaya British forces were aware of the possibility of attack since 6 Dec Singapore time (5 Dec on the other side of the Date Line). As a result PoW and Repulse were able to fire on those first attacking G3M.

Now increase the fleet size and add it to the shore AA defences and the attackers can expect a hot reception.

This would not be like PH at 0800 on 7 Dec.

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If the British are at Sembawang and have twigged that something's up, would they sortie the fleet or sit tight? Perhaps a good first IJN move would be to mine the sole exit from the base.

That would be akin to a declaration of war without any guaranteed kills.

Admiral Beez said:

If the British are at Sembawang and have twigged that something's up, would they sortie the fleet or sit tight? Perhaps a good first IJN move would be to mine the sole exit from the base.

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SaparotRob said:

That would be akin to a declaration of war without any guaranteed kills.

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Might require stealth mining
Mining inside or outside of shore battery range?
Depends on the RN have very few minesweepers or no high speed sweeps on the existing destroyers .

Takes a very brave submarine commander to go submerged into the Singapore Strait.
Japanese ability to drop mines from aircraft from Saigon? and go undetected?

Firstly the IJN weren't into offensive minelaying to any great extent. They had a number of purpose built minelayers as well as conversions, but these were used to lay defensive minefields or were used as transports. Neither were they using their destroyers as minelayers in the way the RN did.

AFAIK the Japanese didn't have air dropped mines in 1941.

The IJN had only 4 minelaying submarines. I-121 to I-124 of the KRS type.

At the beginning of Dec 1941 two of those were allocated to lay mines in Philippines waters. The other pair were allocated to lay minefields between the Malayan peninsula and the Anambas Islands (Force Z sortied to the east of those islands). 3 were used in Jan 1942 to mine the approaches to Darwin and the Torres Strait but these were most of the IJN offensive minelaying activities in WW2 AFAIK.

But consider the problems facing any minelaying attempt. As I noted previously, the RN laid defensive minefields off the end of the Johore Strait, at least some part of which were controlled from the shore, and there were indicator loops to detect submarines trying to enter underwater. Any attempt on the surface would face the defensive guns (15"/9.2"/6") and searchlights. There is a map of the various gun batteries in Singapore in 1941 in this article.

There was also some 18 auxiliary craft for patrol and ASW work and another 17 for use as minesweepers.

We should also acknowledge the issues presented by the fast-flowing and complex currents in the Singapore Strait. Not ideal for precise navigation by a hostile submarine.

Shortround6 said:

..Japanese ability to drop mines from aircraft from Saigon? and go undetected?

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What if the G3Ms were specially equipped?




No one would know it was them.

buffnut453 said:

We should also acknowledge the issues presented by the fast-flowing and complex currents in the Singapore Strait. Not ideal for precise navigation by a hostile submarine.

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That is correct. The last wild Tiger to be found wandering around Singapore island in the 1930s was thought to have been making for one of the islands in the Johore Straits and was pushed off course by those powerful wandering currents.
OT but I recall, as a small boy, our car stopping at night on the main road up country in Malaya, to have the bright reflecting lights of a Tiger's eyes in the fringing jungle pointed out to me.
It brings home to me how much has changed in my lifetime, when I was born only twenty odd years after a wild Tiger was able to wander around Singapore when it still had some jungle. My only adult experience of jungles was Belize where it certainly merited the description "the sauna that bites".

buffnut453 said:

We should also acknowledge the issues presented by the fast-flowing and complex currents in the Singapore Strait. Not ideal for precise navigation by a hostile submarine.

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I wonder if that's why the primary RN submarine base in Malaya was at HMS Pelandok (Georgetown, on Penang Island) rather than Sembawang.

Admiral Beez said:

I wonder if that's why the primary RN submarine base in Malaya was at HMS Pelandok (Georgetown, on Penang Island) rather than Sembawang.

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AB
Sorry but I'm a bit confused. How did you arrive at this information?

AFAIK HMS Pelandok was the Malayan Royal Navy Volunteer Reserve training base and barracks within the Singapore Naval Base.

Penang was never "the primary RN submarine base in Malaya" so far as I am aware. In fact quickly looking through the movements of individual submarines in the Far East after 3 Sept 1939, I can only find two references to them using Penang.
HMS Odin
2 Sep 1939
HMS Odin (Lt.Cdr. R.W. Moir, RN) departed Singapore for Penang. (1)
3 Sep 1939
HMS Odin (Lt.Cdr. R.W. Moir, RN) arrived at Penang. (1)
7 Sep 1939
HMS Odin (Lt.Cdr. R.W. Moir, RN) conducted exercises off Penang. (1)
9 Sep 1939
HMS Odin (Lt.Cdr. R.W. Moir, RN) departed Penang for Singapore. (1)
10 Sep 1939
HMS Odin (Lt.Cdr. R.W. Moir, RN) arrived at Singapore. (1)


HMS Otus
2 Sep 1939
HMS Otus (Lt.Cdr. E.C.F. Nicolay, RN) departed Singapore for Penang. (1)
3 Sep 1939
HMS Otus (Lt.Cdr. E.C.F. Nicolay, RN) arrived at Penang. (1)
7 Sep 1939
HMS Otus (Lt.Cdr. E.C.F. Nicolay, RN) conducted exercises off Penang. (1)
9 Sep 1939
HMS Otus (Lt.Cdr. E.C.F. Nicolay, RN) departed Penang for Singapore. (1)
10 Sep 1939
HMS Otus (Lt.Cdr. E.C.F. Nicolay, RN) arrived at Singapore. (1)

Inter-war the main Far East sub base was at Hong Kong with the 4th flotilla with O/P/R boats and a couple of Cachalot minelayers based on the depot ship Medway. These boats were gradually withdrawn in 1939/40 mostly to the Med. Refits would usually be carried out there or at Singapore.

After Medway and this flotilla were withdrawn it was Dec 1941 / Jan 1942 before any further subs were sent East of Suez. They were Trusty & Truant.

Edit:- Does the confusion about RN use of Penang as a sub base come from Axis use of it? On the basis that if the Axis used it, they must have taken over RN facilities?

Following its capture in Dec 1941, the Japanese immediately began to develop facilities there. That meant moving material across the Malayan peninsula. They didn't open the Malacca Strait to their shipping until Sumatra was invaded, which started at the southern end on 14 Feb 1942. In March 1942 the IJN moved its 8th Submarine Squadron from Kwajalein to Penang to allow its submarines in the Indian Ocean.

Sabang was also used by the IJN as a sub base.

Later in WW2 Penang was used by German U-boats operating in the IO.

History of the Axis base here.