Projekt NM

German Reich (1943)
Self-Propelled Gun Battery – None Built

This vehicle, known only from a single blueprint, is possibly one of the strangest tracked war machines ever designed. German blueprint HSK 3485, dated 15 June 1943, named Project “NM”, shows a monstrous and ungainly vehicle consisting of three Tiger tanks joined together by I-beam girders. Built atop the I-beam frame sits a warehouse-like structure, concealing three 150 mm cannon-armed turrets. The reasoning behind this design, its purpose, and even which branch of the Wehrmacht it was for, remains a total mystery.

Details: Not Many

The only known original document pertaining to this vehicle is a single blueprint held in RH 8/2590K at Bundesarchiv Freiburg, filed under “Wa.Prüf.6 Technical Drawings.” Wa. Prüf. 6 was the central office for the design and development of tanks and armored vehicles under the Waffenamt, the German agency in charge of weapons. The blueprint was drawn in a 1:40 scale and shows a side, top, and front view of the vehicle, as well as details of the doors. The blueprint is only a rough draft, meaning that many components that would be present to make a functional vehicle are not drawn in. Additionally, close inspection reveals faint lines where the design had been erased and changed.

Forming the base of the vehicle are three modified Tiger hulls, each with a U-shaped cutout in the area of the turret ring, which is implied to hold a gimbaling system that supports the vehicle’s frame. The tanks are arranged in a tricycle configuration, with a single tank at the front of the vehicle, and two in the rear. Lengthwise, the distance between the pivot point of the forward tank hull and the pivot points of the rear tank hulls is 14 meters (45’ 11’’). A faint outline of the rear tank hull in the blueprint side view shows that the rear hulls would be able to pitch up to 15.5° up or down relative to the frame. A similar range of motion is likely for the forward tank hull, but this is not shown in the blueprint. It has been theorized that these Tiger hulls would be made out of mild steel of thinner gauge than the normal tank, as the NM would not likely be intended to take enemy fire, and this alteration would save weight. Alternatively, the NM may have incorporated older non-combat-worthy Tigers that were gutted and repurposed.

Forming the backbone of the vehicle’s frame are four longitudinal I-beams, connected by ten transverse I-beams. All of the transverse I-beams sit atop of the longitudinal I-beams, apart from the one at the very rear, which is attached underneath. There are three main transverse I-beams that run the full width of the vehicle and are merely structural to the frame. Three shorter beams, spanning one-third the vehicle’s width each, sit one under each turret, on either side of the main structural member. At the very front of the vehicle and toward the rear, are two sets of two slightly thinner I-beams, which run the width of the frame and attach to the pivoting mechanisms on the tank chassis. The front corners of the otherwise square frame are rounded off into triangular sections. Faint lines on the blueprint evidence that, in an earlier iteration, these triangular sections extended all the way beyond the front of the forward tank hull, and were joined by another underslung transverse I-beam, similar to the one at the rear. This was likely determined to be unnecessary, and the frame was cut back to just meet the center of the forward tank hull. The vehicle would measure about 21.6 meters (70’ 10’’) in total length and 16 meters (52’ 6’’) in total width. Extrapolating from other values on the blueprint, the height of the vehicle can be calculated to be 5.15 meters (16’ 11’’). The bottom of the longitudinal I-beams would be 1,180 mm (3’ 10’’) off the ground. The height of each of the I-beams was 500 mm (1’ 8’’), meaning the frame accounted for a full meter (3’ 3’’) of height by itself. This would mean the top of the frame would sit 2,180 mm (7’ 2’’) off the ground, however, the blueprint shows this to be 2,280 mm (7’ 6’’). Most of the numbers given on the blueprint are approximate values, leading to such inconsistencies.

Mounted on top of the vehicle’s frame were three turrets, each housing a single 150 mm cannon. The central turret was staggered slightly behind the two outer turrets, which were placed just ahead of the rear tank hulls. All three of the turrets faced over the rear of the vehicle. Two 300 mm (1’) tall I-beams are placed longitudinally under each turret. The ends of these beams are shown to be cut down into points; the reason for this is unknown. The turrets rest directly on these I-beams, without any turret rings having been drawn. Should the design have advanced any further, this obviously would have needed to be changed. The turrets themselves measure 3.4 meters (11’ 2’’) long and 2.8 meters (9’ 2’’) wide, tapering toward the front. Each turret has -8° of gun depression, and +10° of gun elevation. The centers of the cannon barrels sit 3.4 meters (1’’ 2’’) off the ground. The distance between the centerline of the central turret and the centerline of either of the outboard turrets is 5.4 meters (17’ 9’’); the distance between the centerlines of the outboard turrets is 10.8 meters (35’ 5’’). Just in front of the outboard turrets, slung between the I-beams of the vehicle’s frame, are a pair of storerooms. It is likely these would have carried everything needed for the vehicle, including ammunition, and provisions for the tank and gun crews. They measure 4.5 meters (14’ 9’’) long, 4.5 meters wide, and 1.2 meters (3’ 11’’) tall.

Concealing the turrets is a simple warehouse-like building measuring 8.4 meters (27’ 7’’) long by 15.35 meters (50’ 4’’) wide, and approximately 3.97 meters (13’) tall. The width of the warehouse is the width of the frame discounting the two outermost longitudinal I-beams. This is a difference of 650 mm (2’ 2’’), which implies the width of the I-beams to be 325 mm (1’ 1’’). There is 1.9 meters (6’ 3’’) of space between the rear of the central turret and the front wall of the warehouse, and 0.8 meters (2’ 7’’) of space between the sides of the outboard turrets and the sides of the warehouse. The warehouse is supported by ten vertical supports around its perimeter, and at least five transverse supports in the roof. The barrels of the cannons protrude past the rear wall of the warehouse and are accommodated by a set of doors each. Curiously, in the forward view of the blueprint, these doors are shown to open horizontally, while in the top right corner of the blueprint an alternative arrangement is shown where they open vertically. The set of doors for the center turret is slightly larger than the doors for the other two turrets, as the center turret is farther away, and thus needs more room around the door to afford its barrel the same degree of traverse and elevation.

User: Navy Maybe?

There are two schools of thought as to what the purpose of this vehicle was. The first is that it was destined for use on the plains of the Eastern Front, but there are several problems with this theory. Firstly, a large warehouse slowly creeping across a field is not very inconspicuous. Second, the NM would be unable to cross rivers, neither by fording, due to its sheer size and ungainliness, nor by bridges, due to its width. On the Eastern Front, it would be relegated to very situational defensive positions, where it could be camouflaged in a position anticipating an enemy attack. The fact that the cannons face over the rear of the vehicle indicates that the ability to quickly retreat (as quickly as such a contraption could move) was a consideration. In a situation advantageous to the NM on the Eastern Front, such as overlooking a large open plain, where its 150 mm cannons would be able to far outrange the enemy, there would be nowhere for the vehicle to run once its disguise is lifted. On top of this, the nearly 22-meter long moving warehouse would be extremely vulnerable to Soviet artillery and ground attack aircraft. There is also the fact that the NM offers zero advantages in this situation over three separate Self-Propelled Guns (SPGs) armed with three separate 128 mm cannons, such as the Jagdtiger, then in development.

The second possible use for the vehicle is also the much more likely one: that of a mobile coastal defense installation. A warehouse perched on a cliff is not likely to draw any undue attention from enemy ships, and careful positioning would allow the NM to extricate itself before the enemy returned fire. Were the vehicle intended for use on the Eastern Front, it would certainly be a project of the Heer (Army), while both the Heer and the Kriegsmarine (Navy) operated coastal defense installations in the west. The name and armament of the vehicle, in addition to its suspected use as a coastal defense installation, point to the NM being a Kriegsmarine project. The name of the project, “NM”, is unlike any project name used by the Heer, and is closer to the naming scheme used by the Kriegsmarine.

The size of the turrets and cannons in the Projekt NM blueprint, comparable to the length of the Tiger tank which they are carried by, puts the cannons as being in the range of large 150 mm’s. German 15 cm cannons are only nominally 150 mm, in actuality, they have a bore diameter of 149.1 mm. Both the Heer and the Kriegsmarine operated numerous types of 15 cm cannons. Through careful consideration of their sizes and service dates, the possible armament of the NM can be narrowed down to four cannons. From the Heer, the 15 cm K. 18 and 17 cm K. 18, and from the Kriegsmarine, the 15 cm TbtsK C/36 and 15 cm SK C/28. All four of these cannon types were employed in some form as coastal defense guns.

The Projekt NM blueprint shows the cannon barrels extending 5120 mm (16’ 10’’) past the front plate of their turrets, and the turrets measuring 3400 mm (11’ 2’’) in length by themselves. This is a total combined length of 8520 mm (27’ 11’’). The 15 cm Torpedobootskanone C/36 is the smallest of the four cannon candidates, at just over 7 meters (23’) in overall length; this is the only one of the four cannons that would fit entirely inside the turret, and allow the turret to be wholly enclosed. The size of the other three cannon types, 8200 mm (26’ 11’’) for the 15 cm Kanone 18, 8291 mm (27’ 2’’) for the 15 cm Schiffskanone C/28, and 8529 mm (28’) for the 17 cm Kanone 18, would necessitate the turrets to be open at the rear, which is common for naval turrets but is contradicted by the presence of an enormous gun mantlet, which lightly armored naval turrets lack. Unfortunately, the Projekt NM blueprint does not show the rear of the turrets, and the details of their construction cannot be ascertained.

Operationally, the NM would likely be deployed to a Seeverteidigung (Sea Defense Zone) where an attack was expected, or where the defense force needed strengthening. The vehicle would be reversed into position overlooking a swath of sea, and camouflaged to best appear as a non-threatening structure. When an enemy vessel came within range, the doors of the warehouse would be swung open, allowing the vehicle’s three turrets to take aim and fire. The NM would probably have time enough to fire a few salvos before the enemy vessel realized it was being engaged by a warehouse, and not by surface vessels or gun emplacements. When the vehicle started to come under return fire, the NM could simply drive forward to move out of danger.

Unsurprisingly, attaching three Tiger chassis together with steel girders and putting three ship’s cannons and a warehouse on top was not seen as a very practical idea, and the NM did not advance any further.

Projekt NM Specifications
Length:	21.6 meters (70’ 10’’)
Width:	16 meters (52’ 6’’)
Height:	5.15 meters (16’ 11’’)
Armament:	3x 149.1 mm cannons, likely 15 cm SK C/28

Sources

Projekt “NM”, Blueprint HSK 3485, 15 June 1943 – RH 8/2590K, Bundesarchiv Freiburg
Der Panzerkampfwagen Tiger und Seine Abarten – Walter J. Spielberger, 1997
Enzyklopadie Deutscher Waffen 1939-1945 – Terry Gander, Peter Chamberlain