Islamic State is using a curious trick to conceal its few remaining tanks, if these two truck containers are a sign. Deep within the containers, recently...

Islamic State is using a curious trick to conceal its few remaining tanks, if these two truck containers are a sign. Deep within the containers, recently captured by Iraqi forces in Mosul, the militant group installed tank turrets and their cannons.

A video posted to Twitter shows the contraptions, most likely built in an attempt to avoid the pervasive overhead surveillance of Iraqi, American and European aircraft.

A tank in the open, with its recognizable silhouette, would be an obvious and priority target for an orbiting warplane. And the turrets look like they once belonged to T-55 tanks, Soviet-era machines of which Islamic State captured several dozen, but the precise type is not exactly clear. The cannons run the length of the containers, which appear to be hooked up to semi-trucks.

It’s a simple concept, and all the militants would need to do is move the trailer into position, open the back doors, fire and then scoot away.

The hidden cannon is not an entirely new concept, but more of a desperate adaptation of an existing “keyhole” tactic — or firing from a position with a line-of-sight toward an enemy while protected by cover or concealment on the sides and rear, and overhead in this case. This makes the gunner visible only to the target, and no one else.

It’s the same tactic, essentially, as a soldier with a sniper rifle firing through a tiny hole in a wall.

#ISIS rebuilt tanks inside a trailer truck to hide it from airstrikes and to move around fast, #Iraq Federal Police has captured 2 in #Mosul pic.twitter.com/Qyl9Qk5vJJ — Iraqi Day ?? (@iraqi_day) July 6, 2017

During the Chechen wars, Russian tanks would frequently reverse into buildings occupied by friendly infantry, requiring Chechen fighters with rocket-propelled grenade launchers to approach directly from the front — a reckless move which they tried to avoid.

Islamic State is using engineering to achieve the same effect. Deprived of sources of weapons abroad and dependent on captured guns and vehicles, the militants have applied skills and tooling inside specialized workshops to all manners of war machinery. Armored vehicles loaded with explosives and Mad Max-style pickup fighting trucks, strengthened with bolted-on metal plates, are common weapons.

The hidden cannon is a low-tech variation on another idea. Seven years ago, the Russian company Novator advertised a version of its Club-K anti-ship cruise missile which can fit inside a shipping container.

Concealed in a port among hundreds of other containers, it’d be practically impossible to find. A flattop warship armed with such containers could be quickly reloaded at sea — simply by flying in new containers slung underneath heavy-lift helicopters.

It’s anyone’s guess how well Islamic State’s container-cannon works in combat. One wonders whether the suspension can handle the shock and vibration of the gun. But as they were captured intact, the camouflage appears to have served its purpose. A tank spotted in the open would have likely been blown away.