. The Monash I tank has a cast hull, with a front mounted engine - think cross between a Merkava and a Sherman, although the root is actually the Vickers Light series so far as the front drive and Matilda/Valentine for the most of the 'tanky stuff'.
It's also an industrial stretch for Australia, like the @ Sentinel, we CAN do it, but it ties up a lot of resources that have a wider use, particularity casting the hulls - so production is a focused thing, we cast up a big batch of hulls but then the line goes away for a long time and isn't opened up again lightly.
-> Therefore when it comes to playing variations on the Monash we don't get to do much to the basic hull.
2. The Australian Army in the post WWII period is organized as two Armored Divisions. Thus we need tanks (Monash) but also the other kit, much of which has to go on the Monash Hull. One of these accessories is naturally an SPG, actually a range of SPG's.
~~~ Lets take a little diversion into Artillery theory and the Tea drinking take on blowing things to hell.
Actually Brit/Cw Arty doctrine, didn't involve blowing things to hell that much. The Royal Artillery bless their Ubique little cap badges, was the one arm of service that actually DID have a doctrine heading into WWII. In WWI they had gone from aiming at the whites of their eyes to some of the most sophisticated artillery work ever employed while expanding exponentially in 4 long hard years - and after it was all over they REMEMBERED! See WWI had proven two things, firstly that you could pump the wealth of an empire into a stretch of trench and you still wouldn't kill everyone and take the damn thing - only infantry could do that. Secondly the job of artillery wasn't really killing people, that was just a nice fringe befit, rather it was all about putting the PBI onto their objectives and giving the support to make sure they stayed there. If you look at the key arty techniques of the 17-18 period it was all about SUPPRESSION, the creeping barrage had more to with obscuring the infantry's advance and keeping square heads down in the bottom of their nice concrete lined dugouts that anything else. OK there were other things, like cutting wire, but the real money was in screening the advance and counter battery fire to prevent others doing unto you.
All this lead to a couple of conclusions that the RA rather took to heart, once it all came down to suppression the size of the shell was less important that the quantity of them and quality with which they were employed, but I don't want to get into the command and control side here. SO quantity, quantity over quality of shells, because a small shell is as effective at keeping peoples heads down as a big one, you can also afford a lot more of them, and more of them is better still at suppressing the objective. This is where we got the (87.6mm) 25pdr in a slot every other first rate European power was filling with 105mm, and it came in 12 gun batteries instead of the usual 8 or 6 gun batteries. So supporting the infantry was about spamming the enemy in modest shells and leaving the killing to the men with pointy things onthe end of their rifles.
Thus an Australian Armored Div needed an SPG field gun, which had to fit on a Monash hull with minimal modification once the turret was removed, because you can't go cutting and welding a cast hull easily. No drama there, the 25pdr in a tin box on the Monash - done deal.
The next key requirement was for a medium piece on tracks, here's where the RA missed a trick @ IMHO. Their needs as they saw them really called for what we'd see today as a modern (post 60's) medium (155) howitzer. But they were used to working within a two gun paradigm in this role with the 60pdr gun and the 6" 26cwt howitzer. See sometimes suppression just isn't enough t0o crack the line and you do need a big (6") shell. And the key to counter battery work is RANGE, lots of range, twice that of a field gun because you need to hit their gun line from you gun line, and a little (lot) more because you get into their medium arty too. Ok I'm not sure the state of the art was up to doing a GC-45 in the late 30's, but they didn't try for it, instead opting for the 5.5" howitzer and the 4.5" gun. The 5.5" was a good weapon, but it copped some backwash form the suppression school, the gun was undersized and its shell was deliberately crap, to keep it cheap. The 4.5" gun was horrid, it's shell was really crap and if it wasn't for the gun's range and a lack of anything better, it would have been a waste of space (slight exaggeration for dramatic effect). But for all this bad press, it was the right answer to the problem (it was just rubbish), suppression doctrine was (most of) the right answer to counter battery fire, we've just given up trying to destroy trenches, blowing pint point gun positions to hell at twice the range is a much taller order, and after all the required result is the enemy arty not interfering with our infantry, so keeping the other gunners heads down works just fine.
Now in TBO, the 4.5" gun vanishes without a trace, the PoD cuts it off at the knees because it was at the end of the queue and had hardly hit prototype form (not even sure it had gone that far) when the Coupe strikes. So we have the 5.5" gun howitzer as the Cw's principal medium piece, even with the PoD, production was already programed to commence in Australia, (and IIRC Canada), the hardware was at a stage where it could be transported - the 5.5" was in play, the 4.5" was not. These leaves us all trying to do CB work with a weapon that only has about 4,000 yards on the field gun (25pdr), not good Miss Jane. It's not a critical issue, so long as the opposition is second rate or equipped to a second rate standard anyway, but against the first eleven, a lack of CB does not bode well.
3. Skipping the Canadians in Russia who are the only ones to actually face this problem first hand, the Australian Army circa 1948 needs a self propelled medium piece, and the 5.5" is the smoking gun - well it would be. but to get formal for a second it is the 5.5" BL gun/howitzer - BL means breech loading (Duh), but in this context it indicates a bag gun, that is the shell gets rammed about three feet up the chamber, before someone shoves a yard long silk sausage full of cordite up the spout. RAMMED - as in with a 5 foot long ram rod (technically a Rammer Staff but lets not get fussy). Now we have to do this within a ~60" turret ring. It's not going to happen, well not unless we take a can opener to the hull and probably splice in another wheel station while we're at it - oh yeah but there's a problem with that. You don';t go hacking into a cast steel hull after its been heat treated lightly, and we're talking about ruining the structural integrity of arse end by turning the stern into a canoe. At this point we really need a new hull, and that is not an eay thing to arange.
~~~ Another diversion, what is the first consequence of SAC's little transatlantic excursion? - Every Heavy AA gun in becomes utterly pointless. I don't mean ineffective, I mean useless, because lets not forget the implications driven by the rest of the air war in TBO. It is a low high mix, and if a gun shooting to ~35,000' isn't much good against 50,000' bombers it is even less useful against swarms of fighter-bombers doing 400mph down in the weeds. I'm not writing off flak here, just conventional heavy guns, stuff over about 90mm that really is that bit too heavy to take into the field and use like an 88.
And speaking of the 3.7" HAA gun, there's two funny things about the 3.7. 1/ Australia has an ample sufficiency of these, we've been making them since 1939 (but don't ask about the Directors). and 2/ they have a flat range, as an artillery piece, of about 18,800 yards - which low and behold is actually a bit better than the 4.5" medium. Better yet, it is a QF with one piece loading, a higher rate of fire and is actually a better supression weapon than the 4.5". It'll be a squeeze but the 3.7" and Monash is a workable combination. Admittedly it leaves the Aust Armd Divs short on a true medium for busting hard targets, but they have these tracked things called tanks that were originally designed for busting infantry though hard targets so all in all as a compromise its not at all bad, there's also not a lot of choice. Not too far from @ either, after the Luftwaffe took its bow the Army's 3.7"s in Europe were mostly used as medium arty in just this way (less the self propelled bit of course).
This is the Nulla I
4. Moving on to Burma, there's a bit of a problem with the Austral-Indian-Thai artillery in this conflict. After the initial period, Burma becomes a very dispersed campaign, lots of people running around everywhere.Little concentration of force in the classical sense because its all about presence and the good guys have to be spread mighty thin to cover the huge area involved. The down side to this, is the ball is in the other court when it comes to numbers at any given point. Our small patrols are always at risk of being out massed if/when they make contact They only protection they can count on is supporting fire and perhaps rapid reinforcement, but its the arty providing most of the security blanket.
However this means that infantry patrols need to be under the arty umbrella and vis a vis the arty have to cover anywhere the infantry want to patrol. All of which ties up a metric shed load of manpower manning the guns and protecting the gunsites which is not available to go out and walk the boonies kicking up bad guys to allow the arty to earn its keep. The demand here is for more range, more range, a little more range and if they could get some range… I think I've labored that point enough. The larger a gunsite's coverage the more economically they can be deployed, to cover either more area, the same with fewer guns or more firepower etc etc. This last brings up another issue, weight of fire. Dispersal means fewer guns can concentrate their fire, quantity diminishes and with it our small but numerous 25pdr shells come up short. Now we need something like the US 105mm M1/M2 series for the extra bang now we have fewer bucks - oh but wait, they have 2,000 yards less range
OK the 5.5" can help a bit, only it's rate of fire isn't great and its only got another 2000 yards over the 25pdr - so at least the 25pdr is the happy mean, 2k more than a 105, 2k less than a 5.5" but its not much help. Nulla is the only light in the tunnel, although there's a fair bit of muck on the headlight. The 3.7" is a high velocity gun, it may or may not have multiple charges by this stage, but it still has crest clearance problems and Burma is a hilly place.
~~~ Yep another side track. What is the second, third, forth things SAC's Berlin BBQ does? Well ok second and third, all the worlds air defence is now so much junk and air defence is THE hot button issue around the world.
Now all this is a bit unfortunate, since all the HAA guns have gone bust, all the fighters run out of puff and Werner Von Braun reached the moon a few years early. I mean ok yes the US is now very keen on not taking that they dispense, but its the rest of us with sh1tting ourselves with fear - Ahh now I remember, that was the forth thing.
So Air Defence or Air Offence if you can pull it off is the new measure of manhood among nations, and lets not forget all those poor frightened urbanites who vote - well in the nice countries anyway. 50'000 feet is the problem, guns are out, fighters need new engines, new airframes, and missiles, missiles are the coming thing, but they have a LONG way to come. The bulk of human expertise in this area is now air pollution. Oh yeah and the bulk of all human technology is tied up in the one country the rest of us are dropping darkies over. Hmm….
So there's a lot on the line here, we , as in the rest of the world, have to bootstrap the technology to get only thing that counts with the voters and the the world megapower. Worse until we do get enough enough millimeters on the ruler for SAC to even notice, its hard to get the political traction to leverage into the technology to….
So what was I saying about guns again? Well they're pointless, 50k is not impossible, but hell by the time the guns would have a chance, they'd be within SAC's blast radius. Still something is better than nothing, it reassures the voters at least and hell if we could get a shell up there SAC'd notice, even if only to laugh, and I suppose any attention is better than no attention.
5. Now @ the old 3.7" ran to six marks, we built the Mk.1, the Mk.2 was some minor mods, Mk.3 was a mesh of the two, the 3A had some more fun on the old fiddle. But things got interesting from, the Mk.4 on. See the UK had this habit of making AA guns by necking down a big existing cartridge down to a small existing caliber, the Germans were dabbling in high altitude flight (as was everyone else) and there was this Major at Woolwich by the name of Probert.
The Mk.IV took the RN's 4.5" gun and linered it down to 3.7" and it worked ok. The Mk.V finessed the Mk.IV but wasn't quite what the doctor ordered. So the MK.VI took a new departure, this time they picked the 5.25" off a KGV and piped it down to 3.7" - sheeze talk about overbore, makes Wetherby look like a wimp.
Anyway Major Probert came up with this unify rifling scheme that minimized wear from pushing five ton of cordite up a 2" straw, and produced a smooth very aerodynamic shell, just the ticket for this sort of thing. So I flipped a coin, Heads Probert got out to Canada, tails he didn't - just to be fair it was best of three. Honestly no one was more surprised than me to find he really learned to love Maple Syrup. Seriously he was a boffin on staff at Woolwich, they would have got him out.
Now comes wars end the Canadians wouldn't give much of a damn about SAC, and there's just no work for him in the UK. But down here, we've got the the Japanese keeping us focused. We don't make the 5.25, but we've got 4.7"s and 6". Now if we took a 5.5" outer jacket, that's the 5.5" medium gun from earlier, with a 60 caliber 3.7" tube and the result looks very much like the @ 3.7" Mk.6 without the excess bulk of the 5.25 - @ they needed the mounting as much as the gun/cartridge combo. The other thing is Australia isn't wedded to cordite by war's end. Half out contribution to the war effort is churning out Russian ammo and raw explosives ect, and a huge slice of our wartime growth/investment has been in the chemical industry.
50,000 feet is on the cards, may be more, may be close, it hardly matters in the end, its a fig leaf and insurance and we build three/ four batteries of them for Sydney, Brisbane, probably never even install Melbourne's, and the rest never get built.
Of course the whole lot are obsolete even as scarecrows when Jabiru comes along in the late 50's. So they get greased up and put to one side….
6. … and in 1961-2 the Army start looking for something with really long reach.
Granted I just said you couldn't shoehorn a 5.5" into a Monash, but I didn't say anything about ON did I?
The 3.7" QF Mk.5 (Aust), comes on a high angle base ring (CP in Cw speak) mounting, intended to be bolted firmly down on a big slab of concrete. It's also going to be fully power worked and probably weigh something like 20 tons. Strip off all the crap and it might hit 15 - if we're lucky. This bolts down on top of a spare Monash chassis with a fold out platform and some hefty stabaliser jacks. Rolling weight less barrel about 5-8 ton over standard tank. The tube alas has to travel separately - towed by the same take if we're lucky. It is a big fat horrid abortion that can reach out to 32,000 yards with a 31lb shell. it is just viable in a semi-static application as found in Burma, but no one loves it.
it'll probably take a year to meld the two together properly, with limited traverse over the front of the hull - Nulla II, and thanks for your time