We can be a bit more specific as to the forces involved in PNG at least and their make up.
The main offensive land force available to 17A from April '42 through to December was built around a special service group now known as the South Seas Force (or Detachment), which was a composite of a naval special naval landing force (SNLF) and a composite army unit built around the IJA 144 Inf Regt. There were significant numbers of Korean and non-combatant labour units attached to the force, as initially it landed at Gona (and later at Milne Bay) with the intention merely of building advance airstrips. With the failure of Mo the 17A was tasked with the near impossible task of attempting an overland capture of the strategic port of Moresby. no other army in the world at that time would have even attempted such an undertaking. Whatever you say about the poor showing of the IJA, these guys had the gonads to take on what any other army would consider to be an impossible task. They through into the battle basically a brigade sized force, half of which (the SNLF component) were highly mobile, but very lightly armed elite troops.
A look at the TOE of the heavy component of the force (built around 144 Regt) reveals or gives a good indication of the artillery types they were throwing into this battle. the following is from a TOE report just after the capture Guam, ie just before redeployment:
The sSF was brigade sized force formed under the direction of the IJAs jungle warfare expert (col Tsuji) intended to be used in the Japanese seizure of the Sth Pacific. Everything about it was specialised, from the footwear issued to the troops (split towed, lightweight canvas as opposed to the heavy and slippery hob nails used in the Allied clodhopping armies sent to oppose them), to the make up of the force itself. Initially it was tasked with the the capture of islands in the sth Pacific, as well as Wake, Guam, and the Gilberts. We often hear about how badly the US and allied forces were outnumbered in these battles, without acknowledging that in truth, the Japanese in this TO were outnumbered about 4 or 5:1. The forces used to capture rabaul for example were outnumbered by the allied ground forces by about 3:1. This was never battle fought on equal terms in sheer numbers.
The army component of the SSF was drawn from the 55th div and was commanded by Major General Tomitaro Horii. It consisted of the following units:
- 144 Inf Regt with 2700 men
- 1st Battalion of the 55th Mountain Artillery Regiment with 750 men and 12 75mm mountain guns (type unknown)
- 3rd Squadron 55th Cavalry Regiment
- 1st Company 47th Anti-aircraft Artillery Battalion
- Reinforced Infantry Gun Support gp (which I think had 12 70mm IGs).
- Infantry gun support gp for the SNLF detachement (maybe 12 guns)
- plus Engineer, Communications, Transport and 3 Medical detachments.
The detachment was to be used to seize Guam but was diverted to Wake after the initial unsuccessful attempt by the navy to seize the atoll, where it suffered some casualties (I believe these were made good before deployment to PNG). It later rejoined the 55th Division in 1943 for the NG campaign.
On May 4, 1942, troopships bearing the South Seas Detachment set sail southward from Rabaul for Moresby . Three days later, however, a naval engagement appeared to be brewing in the Coral Sea; whereupon the transports immediately veered back to the north, in order to avoid combat. The Japanese failed to secure victory at coral sea and this caused no small loss to the Fourth Fleet. Plans to land the South Seas Detachment directly at Port Moresby from the sea had to be abandoned.
Imperial General Headquarters, on May 18, 1942, issued an order of battle for the Seventeenth Army, to be commanded by Lieutenant General Haruyoshi Hyakutake. An Army in name only, it was made up of several infantry regimental groups:
- 35th Infantry
- Brigade less 114th Regiment
- South Seas Detachment
- Aoba Detachment (built around 4th Infantry Regiment)
- 41st Infantry Regiment, etc.
The mission of the Seventeenth Army in Operation FS was the capture of strategic points on New hebrides islands, new Caledonia, Fiji Samoa, Tuvalu, Tokelau, Tonga, (some sources also say they identified the phoenix islands as an objective). Before any of this 17a was tasked with the capture of Moresbey, at that time defended by a brigade group of the Australian Army.
The objective of these operations was to take possession of strategic island points in order to intensify a cutoff in the contact between the US and australia, while squelching the Americans' and Australians' plans of counterattack from the same areas. Action was slated to begin about the beginning of July 1942.
The objectives were totally unrealistic and a reflection of the dreamworld IGHQ was living in. but the campaign in PNG was to show in spades the disparity in quality between the IJA and their allied opponents at that time. With not much more than a reinforced brigade of troops....about 7500 men, they took on firstly 1 Australian div, then a second Australian Dive then an American Div and finally a reinforced US RCT. in the end, the Japanese forces were utterly defeated, but not before they came within an ace of doing the impossible. the differences I believe can be traced to two critical areas, their ability to get meaningful artillery support into the Jungle, and the amazing mobility their light troops enjoyed with their special kit and doctrines. the Japanese used in their famous flanking moves carried no rice, ammunition only, were very lightly dressed and specially equipped with jungle footwear. time and again they were able to outflank and make obsolete position after position. Time and again the US and Australian positions were pounded by these so called obsolete, useless pieces of artillery which the allies with their "mortars" could not answer. most Australian vets that fought in that campaign that ive met express the envy thay had that the Japanese had Ig support and they had nearly useless mortars only. Moreover, well into 1943, the allies still could not bring to bear heavy weapons into the jungle. Similar things were happening in Burma. My best estimate is that the allies needed odds of 10:1 + in the jungle plus complete air superiority to defeat a properly supplied Japanese force, and this disparity remained the case well into 1943. trouble was, by the end of 1942, a 'properly supplied" Japanese force was all but a memory....
The allies overcame this in a number of ways. in the PNG jungle the Us basically retreated except for a few units. it was too costly and too unproductive for their liking. The Australians, after gona set up their jungle warfare school at Canungra in qld and used surviving veterans to train follow up units. gradually the Australians learnt the difficult art of jungle warfare, that stood them in good sted right through to today.
The Americans learnt a different path, take only what you need, use seapower and air power in place of artillery and blast all opposition out of existence before walking in and taking what you want. Inelegant, but effective I guess.