I have already described what I'd like to see in my ultimate infantry fighting vehicle in the Ultimate Gavin page. Since then I have been meditating on what sort of light tank should accompany it. Using the same basic hull as described in the Ultimate Gavin page less the hull firing ports / armored windows I'd then like to describe what I'd add on top of it to make it the ideal "street fighter" light tank.
1. As the name suggests, the first order of business is to remove the perfectly good and functioning turrets of our remaining quantities of M551 Sheridan light tanks from their worn out, tired hulls that after 35 years of fine service need to be put out to pasture. The thing I like about the Sheridan turret more than anything is it's massive - perfect for "street fighting" - 152mm gun which has both a HEAT round big enough to do in any MBT out there and a huge APERS round with 17,000 (yes, that's right!) flechettes. It even has a through-barrel laser-guided ATGM but I've heard bad things about this gunking up the barrel so bad it needs a thorough cleaning before you can fire anything else from the gun, so that isn't really on my radar screen. The Sheridan's turret has internal storage for 28 rounds, plenty considering how big they are. Now why is this gun so "perfect" you say? Well this is such a big gun that the only known time (at least for me) they were ever used for MOUT - in Panama - one shot took out the entire corner quarter of a several-story building without trouble, causing all Panamanian resistance to cease and desist right then and there. Another anecdote is that the main gun round is so big that wile most (120mm or so) tank guns are expected to be about to produce a 'mouse hole' (a hole large enough for a man to crawl through) in the side of a building the Sheridan's main gun can produce one large enough for two men to walk through side by side! Is that a fabulous piece-of-shit or what?! During WWII the Germans found that a approximately 150mm gun was the best for MOUT, not to small as to have to minimal an effect (in MOUT you want a "demolition gun") yet not to large that it would have too little ammunition. The Germans had a 15cm "infantry gun" that they used to devastating effect. Now heavy-tanker types out there might think that in order to get such a big gun you have to have a low velocity gun, a definite no-no to them. Well there is only one reason to have an HV gun and two reasons not: the reason for is to maximize armor-killing ability (presumably through an APFSDS round) and the two reasons against are that minimizing your caliber minimizes your infantry-support abilities (the MAIN PURPOSE OF A TANK!) and that a larger HEAT round is just as good as a smaller APFSDS round in armor-lethality. So they equal out yet the large-caliber LV gun is better overall.
2. Next step I would take would be to place a ACAV-style gun shield on the commander's copula and MG (not the Sheridan's historical monstrous gun shield) and then add another MG to the loader's (or what I think is the loader's) hatch and also give him a ACAV gun/copula shields. Now both of these MGs should be 7.62mm to standardize ammo types. Just like the "Ultimate Gavin" I would have a driver's transparent-mounting-ball "bow gun" that he could use when the vehicle is halted (and his hands are free) for forward suppression when the vehicle is at it's most vulnerable. the bow gun would have 1,000rds, the "wing guns" 5,000rds each and the 7.62mm coax MG 15,000rds (recommended amount by combat-experienced tankers!).
3. I would next install a small firing port and armored window similar to those found on the hull of the "Ultimate Gavin" on the rear of the turret for buttoned-up rear defense (though it would only take less the 4 seconds for the turret to traverse 180 degrees). However if this is not really possible for some reason (vital, immovable item inside is in the way) it is vary much optional and doesn't need to be done.
4. Finally I'd like to add a 60mm "assault mortar" mounted on top of the main gun. This would be fixed at a 65 degree elevation (because mortars usually have 85 degree maximum elevation and the Sheridan's gun has a max elevation of 20 degrees, this to allow use at minimum ranges) relative to the main gun's barrel and would have a small long-rectangular "hatch" large large enough to fire and load the mortar through. the mortar would be adjusted by the gunner, fire commands would come from the commander and would be loaded/fired by the loader, just like the main gun. The mortar would be a variation of the current US standard M224 light mortar but with one major modification: the barrel would be cut in half and it could be used either in the short-barrel "assault" mode or the longer barrel "emplaced" mode. The two halves would screw together to create the longer "mode", which would use the standard light bipod and baseplate and have longer range (probably even longer minimum range). The shorter "assault mode" would be short enough to be loaded from within the turret (with a little hand/arm contortionism from the loader) and the longer "mode" would have the muzzle stick outside the turret, then usually with the loader handing the ammo to the commander for him to load. Somewhere inside the turret the 60mm mortar ammo would be stored, for now I do not know where, and I'd hope there would be enough space for about 150rds. The mortar would be fully dismountable and an assault baseplate - for use with the short-barreled "mode" - or a semi-permanent baseplate, bipod and barrel-extension - for use with the longer-barreled "mode" - would be stored on board. The mortar would be attached to the barrel of the main gun at the muzzle and breach-swivel-joint with quick-release devices. Other than the approximately 15cm LV "infantry (support) gun" the 60mm mortar is the most proven "heavy"/crew-served weapon in the modern MOUT history. Larger mortars use up ammo to quickly and are not transportable enough and anything but a mortar dose not have the necessary angle-of-fire to fire from one street to another: howitzers and rockets do nothing but create rubble for the enemy to use as ready-made fighting positions and obstacles that not only produce lots of dead/homeless civilians / bad press but also make assaulting a urban area go from difficult to near impossible without exorbitant casualties (look at Stalingrad, Berlin or Manila in WWII!). At minimum the Israeli's, as usual, have beat us to this game and already have a 60mm mortar in their Merkava's turret for precisely the reasons I argue.
Like the Ultimate Gavin all MGs are removable and kits are on board for dismounted use. This is to make sure that if a vehicle is hit any salvageable parts can rapidly be cannibalized on-the-spot, the most useful of which parts are weapons, ammo (if not destroyed), fuel (ibid) and routinely replaced vehicular parts, such as road-wheels, track links/belts, suspension system parts ect.
Mike Sparks predicts the next Normandy Beach will be a city, I fully agree with him. We need vehicles with from-the-ground-up-designed-for-city-fighting features so we can win that fight with a minimum of casualties, not the SPR-like destruction of men which wile we ultimately prevail we will loose since the enemy has won by making the whole operation unjustifiable to a casualty-shy public at home. My STUG and Gavin designed are doable today with a minimum of cost ($500k max with conversions) with existing equipment, vehicles and resources - nothing new to invent - to win in Iraq, Afghanistan and any future conflict with equipment and techno-tactics perfected by the Israelis, who have to face this stuff for real every day.
NOTE: For those not aware the name Stug has historical referenced relevant to my light tank design. The Stug was an abbreviation of a long German word used by the WWII German Wermarcht for an infantry-support self-propelled-gun that was light, low profile, easy to produce, highly adaptable, vary reliable, usually had a bigger gun that it's equivilant-sized turreted-tank and was generally a great thing to have around if you were an infantryman. In honor of the idea of the "Stug" I name by new infantry-support light tank with a huge gun and plenty of other infantry-support weaponry the "Stug".