The Strait of Hormuz is too big to support the largest tankers in the world, but too narrow to make submarine hunting a doubtful undertaking.
That incongruity is the engineering context of the Iranian reputation of the “black hole” under the sea: not a single flawless vessel, but an array of platforms that have been adjusted to a narrow, clanky, elongated, electrified chokepoint where a merchant fleet is forced to operate in known lanes. A diesel-electric submarine, which is able to come to a halt, listen and wait, acts less like a moving object and more like a section of seabed, which every now and then moves.
Majority of the work is done by geography. The Strait, 82 feet to 131 feet, of the depth, occupies a mean twenties place: easy to surface ships, yet limiting to submersible marine vessels, which desire the vertical space in which to maneuver, and intolerant when powerful currents cause a hull to deviate on a course of choice. Incorporate heavy commercial traffic, omnipresent machine noise, the sonar search noise of an acoustically shallow basin, and the traditional benefits of wide-area sonar search have been boiled down to a small-scale, resource-heavy issue.
The most technically interesting conventional submarines still in Iran are the three Kilo-powered Russian-built boats which are locally known as the Tareq. Each is about 74 meters in length, and carries 18 torpedoes in six 21-inch tubes, and interchangeable in torpedoes and mine loads. The limitation of their payload is not their fundamental limitation, but rather that of their geometry: they can only safely use their stealth at a depth of about 150 feet forcing their comfortable hunting ranges down deeper into approaches like the Gulf of Oman. Despite this constraint, their presence alone increases the range of the so-called “possible ambush waters,” which escorts and patrol aircrafts have to clear, patrol or just accept as uncertain.
Iranian indigenous midgets and coastal submarines would be the boats that are more suitable in the shallows of the Gulf. The Fateh 48 meters and 600 tons submerged (approximately) is designed to have extended patrol capability than a midget but still fits into regional littorals. The value of the platform is industrial as much as tactical: it represents an indication of the recurring construction of domestic submarines and a transition toward complete reliance on imported hulls. Another Iranian innovation to demonstrate air-independent propulsion plug on a Fateh variant-An effort to increase the time that a submarine is submerged and minimize the instances when a snorkeling exposes the location of a submarine.
Then there is the Ghadir-type midget submarines which is the most natural type of the fleet to fit in the tight spaces. Small boats are able to take advantage of bottom shapes, approaches to ports and masking properties of coastal noise, such as the possibility of lying on the seabed at areas where bigger submarines cannot safely navigate. According to one former Iranian sea leader, the Ghadir-type can perform anything the U-boats did in World War II, a distortion actually meant to be commerce-pressure rather than fleet-to-fleet.
The effects of “black holes” are amplified when submarines are considered as a single layer in a larger denial architecture. Combining mines, coastal anti-ship weapons, fast attack crafts, and surveillance assets with the ambiguity of underwater makes the defenders conduct slow and methodical clearance and verification missions. Iran has also announced Hoot supercavitating torpedo concept, with speeds over 200 miles per hour; the problem with operation lies in the less frequent use than the planning load of the short-warning threat in restricted water.
To navies charged with ensuring traffic flows, the engineering problem is enduring in nature: the physical constraints of the Strait make uncertainty a weapon and a mixed submarine force of the Iranians is optimized to ensure that the uncertainty is maintained.
