Let’s have a look at some Russian sources on this. The history of the T-54 tank started in the Fall of 1944, when the Nizhny Tagil designers created as a “side project” a proposal for very strong modification of the T-44 medium tank, designed to further improve the protection and firepower of the T-44 while keeping the adequate level of mobility and terrain passability. The first documents and drawings were shown to the Tank Industry Commissariat in the last days of October 1944 and on 1st of November 1944, the comissar, V.A.Malyshev signed an order for the Plant No.183 to create a prototype.
让我们在毛子的来源那边看一下。T-54的历史是从1944年秋天开始的，就是当下塔吉尔的设计师们搞了一个在增强T-44火力的同时又能够保证适当的机动以及地形通过能力的T-44魔改版的一个“副产品”。在1944年10月末以及1944年11月1号，第一批文档和草图被递交给了坦克工业军需部以进行查看。V.A.Malyshev政委签署了命令，让183号工厂生产一辆原型车。 

This first project wariant still lacked many of the advanced features. It used the old transmission and old tracks, but despite that the first prototype went to trials in the beginning of 1945. In February 1945, first factory trials of the prototype took place. This new vehicle, in accordance with its purpose, was heavily armored. The frontal plate was 90mm thick (according to different source however, the frontal armor was 120mm thick), the sides were 75mm thick and the rear armor was from 35 to 45mm thick. The turret was sloped to the back somewhat and the driver’s hatch was in the sub-turret armor plate. This is the armor schematic from the alternative source:
第一份计划还是缺少许多先进的玩意。它用的还是旧的传动系统，旧的履带，但是尽管如此这第一辆原型车依然还是在1945年初投入了测试。在1945年二月，这辆原型车的第一次工厂测试开始了。这辆新车正如其原目的所注一样，防护非常的好。正面装甲板是90mm厚（然而有不同的来源指出正面装甲板有120mm厚），车身侧面厚度是75mm，车后方的装甲大概有35~45mm的样子。炮塔有点向后倾斜，驾驶员的舱盖也是放在副炮塔的装甲板中的。这是其他来源中给出的装甲分布图：

The 120mm armor is however mentioned more times, so it’s possible that that number is more likely. The frontal turret was either 160mm or 180mm thick (varied from prototype to prototype).
然而正面是120mm的说法被提到了更多次，所以很有可能其实真的是120mm。炮塔的正面装甲要么是160mm，要么是180mm（每辆原型车都不同） 

The vehicle was powered by a V-2-44 520hp diesel engine, that, thanks to the way it was positioned in the hull (across), allowed for significant savings of internal space. The suspension was completely taken from the earlier T-44 (five roadwheels on torsion bars per side). The vehicle weighed 35,5 tons, maximum speed was 44 km/h.
这辆车是由一个520马力的V-2-44引擎提供同理的。由于该引擎的摆放方式（横着放的），该车节省了大量内部空间。悬挂系统是直接从早期的T-44上拿来用的（每侧的扭力杆上都有五个负重轮）。车重35.5吨，极速是44km/h

The main gun of this tank was the 100mm D-10T-K gun, this was actually the first time a regular Soviet tank (without strong modifications to the turret) could carry a 100mm gun. The D-10T-K variant different from the original D-10T with the lack of the spring counterbalancing mechanism – in order to balance the gun, certain parts were made lighter instead (and certain parts were made heavier). The D-10T-K gun could fire an AP tracer round BR-412 and penetrate 120mm of armor at 1000 meters. The later 1945 prototype was apparently equipped with a LB-1 gun.
这辆车的主炮是10mm D-10T-K炮，这其实是苏联第一次有了能在不进行对炮塔魔改的情况下就能装上100mm炮的常规坦克。D-10T-K炮与原版的D-10T炮的区别是没有了弹簧平衡机制—现在为了平衡这杆炮，部分零件的重量变轻了（部分零件变重了）。D-10T-K炮可以发射BR-412 AP弹，并且可以在1000m外击穿120mm的装甲。1945年后期的原型车用的是LB-1炮。

Silentstalker: two things – first: for the game purposes, this is just a regular D-10T gun, balistically it was the same. Second: just to be clear, the counterbalancing does NOT mean gun stabilization.
SS注：两件事—首先，出于游戏性考虑，这杆炮肯定只是常规的D-10T炮，应该是差不多的。第二：澄清一下，平衡机制并不意味着主炮的稳定性。

The new tank was brought to Moscow on 22.2.1945, where it was introduced to the chiefs of tank industry and the military. On 11.3.1945, trials at Kubinka proving grounds started and they took a little over a month. During these trials, the prototype managed to drive over 1500 kilometers and the results were clear: T-54 was superior to all contemporary Soviet tanks. The testers did notice some issues however and suggested fixing them, notably the turret design, use different type of tracks, switch the transmission for something else, to equip the tank with anti-HEAT spaced armor plates and to update the set of optics (both gun and vision) to something modern. The Plant No.183 complied and by June 1945, two more prototypes were built with over 60 various improvements. One of them had planetary transmission, the other had planetary steering system. The second prototype was deemed more perspective and was heavily tested. Further improvements were made (at that point around November 1945, over a hundred), which resulted in what we know as “Model 1946″ (basically, a stock ingame T-54).
新的坦克在1945年2月22日被带到了莫斯科，在那里它被介绍给了坦克工业部以及军事部的老大。在1945年3月11日，这辆车在库宾卡试验场开始测试，实验持续了一个月多点。在测试中，这辆车能够驾驶超过1500km，结果也很明显：T-54比现在苏联的所有坦克都要好。然而测试人员的确发现了一些问题，并要求修复它们，其中包括炮塔的设计，换一种履带，把传动机制换掉，给坦克装上间隙装甲以抵抗HEAT弹，以及把光学瞄准镜（主炮的和观测用的）换成更现代一些的玩意。183号工厂收到命令后开始改装，1945年6月，已经有两辆搭载了60多处改进的原型车被生产了出来。其中一辆有行星齿轮变速箱。而另一辆有行星传动系统。第二辆原型车受到了更多的重视，也进行了大量的测试。此后又进行了大量改进（在1945年11月左右已经有超过100处改进了），它的结果就是我们现在所知的“1946版”（就是游戏里的白板T-54）