This is an idea that I have touched on on several other pages but I've decided that it warrants an entry of its own. Carlton Meyer makes a good case for a system he calls the Artank. Some equally valid objections are made here too. In fact Artanks have already seen service. Some M4 Shermans were armed with 105mm howitzers. Many Sherman Battalions had six such vehicles (then termed "Assault Guns"), three as part of the HHC and one with the HQ platoon of each Sherman company. Incidentally, some such battalions also had a company of M5 light tanks and a squad of three 81mm mortar carriers (often half-tracks) It is not possible to place a bigger gun such as a 155mm Howitzer on a tank like the Abrams without significantly increasing the height or bulk, reducing the armour, increasing the weight and/or reducing the ammo load. My personal suggestion for this concept is to forget about trying to mount a howitzer in a tank turret and instead create a vehicle of Assault Gun configuration. By doing this not only is production simplified, but the vehicle can mount a far greater level of protection for a given weight.
My crude illustration shows a 155mm armed vehicle based on an M1 Abrams hull. This is rather like the ISU-152 Assault guns used by the Russian army in World War Two, but our modern version would have a greater degree of elevation to increase its indirect fire capabilities.
Unlike SPHs such as the Paladin and Crusader the 155mm Assault gun will have sufficient protection to undertake direct-fire missions against enemy bunkers and vehicles. It can start "thinning out" enemy formations long before they are within tank gun range. The Heavy Assault gun can attack certain targets with "plunging direct fire". It can also use a range of ammunition not available for the 120mm tank gun. For example, to suppress an enemy ATGW position assault guns can use their indirect fire capability to attack it with Air-burst HE, WP and Anti-personnel/Anti-vehicle DPICM rounds.
Two variations of Heavy Assault Gun suggest themselves. Several nations have been looking at 140mm Tank Guns. These promise to be potent weapons but the weight of the rounds requires that the vehicle have an autoloading system and the bulk of the ammo will limit the number of rounds that a vehicle can carry. While the 140mm gun can be fitted to a tank turrets the size and weight and the need for an autoloader make the practicality of this questioable. A better option may be to mount the gun in an assault gun configuration vehicle which can support 120mm armed tanks with high velocity direct fire and will also be capable of high elevation fire. At present no Guided projectiles in 140mm currently exist and other types of ammo are currently limited to anti-vehicle types.
The other variation is to create a Heavy Assault Gun using the same 120mm weapon as used by conventional tanks. The Assault Gun configuration would allow more ammunition to be carried and allow the gun to be mounted so that it can be fired at higher elevations than are possible with a 120mm mounted in a conventional gun turret. This option simplifies logistics since both the tanks and Assault guns use the same ammunition.
FEEDBACK Respected Veteran Gunner Larry Altersitz writes:- I'd try to slope the glacis plate more, but that's minor. Might consider a 7.62mm minigun/40mm HVGL Cobra-style turret for the commander position, also. That gives a little more support to the entire unit against infantry, snipers and RPGists. Go with a big diesel in lieu of the gas turbine; saves much fuel. You'll need some sort of material handling equipment on either the assault gun or its ammo vehicle to load projectiles/ powder. The engine in the rear precludes standard howitzer access for ammo. Might need a single, bigger top hatch to make re-arming easier. Real good candidate for a tank roof that can swing out of the way for re-arming.
PW: On the rear deck of the vehicle I've drawn a simple conveyer belt that would allow ammo to be rolled right through a hatch at the rear of the compartment. Assault Guns would probably include Assault Gun Support Vehicles. These resemble IFVs but carry ammo in place of the infantry. As well as providing a ready re-supply they also act as the Assault Gun's "Wingman", providing local defence.
Carlton Meyer, Editor of G2mil, comments:- Has anyone ever considered a barrel extension? Rather than long awkward barrels for most rapid fire missions, use a shorter one, which is good for close direct engagements too. If you need to fire beyond 30km, the crew takes the extension off the roof and screws it onto the barrel to give it 10km extra range.
PW: This poses the interesting question; would a 155mm Assault gun really need to fire at targets beyond 30km that often? Probably not as part of a Heavy Armoured task force. The longer barrel could be added if they are used as more conventional SP artillery. That barrel extension could also double as a snorkel during wading operations.