Huh?!
Assault rifles, APCs, heavier RPGs/bazookas, and logistical reorgs increase the fighting power severalfold. Transistors, improved spy planes, and improved communication technology upgrade C3I tremendously. Tank armor is thicker and the designs are greatly refined, including the use of adapted ammunition (HEAT rounds etc.). Improved ranging and sighting technology also makes them more effective at night as IR technology is in its infancy. Synthetic technology is greatly increased, allowing these armies to stay in the field longer with more gas and supplies. Flak jackets and rudiments of bulletproof armor are starting to become known. Interceptors might have short legs but they are better in 1950s than in late 30s and the planes are much more effective (I'll take an F-84 or F-86 to 2 Bf109s anyday) Tactics have changed greatly as well.
1955, not 1965
Assault rifles? Not yet. The AK is not in general use.The early models has serious issues with the receiver (among other things). They didn't start to reach the field in any number until '56/'57 onwards. The Eastern block is still using the SKS and Bolt actions (along with the PPsh-41 SMG). U.S. is still using the M-1 (M-14 didn't enter service until 1957). The FN-FAL is entering service, but there are still LOTS of bolt action rifles on the continent
APC? Sort of. The BMP 50 is replacing the BMP 40 halftrack, but it is till open topped and the armor is more than suspect. The U.S. is beginning to deploy the M-59, but it is not in full use, most troops are still in 6x6s or on foot.
Improved Spy planes? Compared to WW II, a bit, but not very far. The Mosquito was just as capable as a RF-94 & the wooden plane had longer range. The pictures are better, but the tech to use them is barely advanced from VJ Day.
Tank armor? It is indeed thicker, and the tank guns have also increased is size and pentrating power. Aiming & firing is still very much a stop to shoot or fire on the move and pray game. The USSR has just begun to deploy the T54/55 & the U.S. is still using the M-48. The British have the best armor of the time period in the Centurion. Yes, they are better than their WW II counterparts & would easily defeat a Sherman or Panzer MK IV, but they are no more lethal to other tanksof their day than their older cousins. It wasn't until the late '60's - mid 70's that the "one shot, one kill" era started & until the introduction of the M1A1 and Challenger 1 & 2 the tank was still vulnerable to infantry weapons (and, based on some of the recent results from Iraq, may be getting vulnerable again)
Aircraft? I would rather be in a F-86 than a Bf-109 as well. Problem is that BOTH sides are equipped with 1955 gear, so the other side has Mig -15 & -17, with the American Century series just starting to come on-line with the F-100 SuperSaber. With the early jets you didn't have the range of the Mustang and air-to-air is still a gunfight. Jets (well,second generation jets) can carry a heavier load, but they also take longer to build & there aren't as many jets around, the lethality jump just isn't there, not compared to the damage that could be wrought by the swarms of JagerBomber or Il-2s of the war years. The great changes will come later, with guided weapons and sub-munitions.
Night vision? Not yet. The first practical starscopes made there combat appearance in Viet Nam. The IR of the era was crude, unrealiable and thin on the ground.
Transistors had barely begun to enter the battlefield in 1955. Virtually all radios and radar scopes still used tubes (hell, the Mig-25 IIRC had some tubes in the electronic suite up to the '70's). The miracle of modern tech, the guided weapon, has just begun to take it's first baby steps.
The biggest thing that hasn't changed in any significant way is the true killer of the battlefield; artillery. The majority of tubes are still towed, the supply train is still weak (even most of the weapons are WW II holdovers) There are still lots of 75mm in the park, with the 152mm & 155mm still semi-rare. The MLRS system is decades away, even the sub-munition won't be introduced until the late 60's (well the M-444 did come into use around 1962, but it wasn't really a DPICM).
It was only in the late '60's and later, generally much later, that the modern, almost impossibly lethal, battlefield developed. A non-nuclear war in 1955 would have been bloodier than the 1942 version, since tactics had evolved, but it would, as the original question asked, be just as sustainable in terms of ground and air combat and the ability to resupply.
This is the difference from today, where a major ground war between the major powers would be over in weeks, possibly two months at the outside. After that, the modern battlefield would be swept clean of the living and there would be no way to get new troops trainedand equipment built fast enough to make good losses.
The naval part of the battlefield was intentionally omitted by the original poster. This is, to a degree, regrettable, since it is in the naval arena that warfare actually evolved the most in the post WW II decade (and with the introduction of the SSN in 1954-58, was revolutionized).
