The basic problem of modernising midget submarines is that they are short-life craft, comparatively easy to build and too small to permit installation of extra equipment to extend capability.
Having said that, the technology of midget submarines is advancing to keep pace with the growing awareness of the value of clandestine underwater activity. Many navies operate such craft, but not all disclose the fact they do. Some navies use them to deploy ''combat swimmers'' for sabotage missions, others to reconnoitre hostile harbours and coastal waters. The most notorious are the as yet unidentified intruders in the Swedish Archipelago, which have been confounding the Royal Swedish Navy's best countermeasures for some 15 years. Another important group are the submersible rescue vehicles, used to rescue survivors from sunken submarines. These are not armed, for obvious reasons, but they employ even more advanced technology as they must operate at maximum depth.
The Russian Malachite Marine Engineering Bureau, based in St Petersburg, is marketing the Pyranja midget design, a derivative of the Project 865 Losos type built for the former Soviet Navy. Pyranja is a small four-man boat with a normal displacement of 250 tonnes. She can embark up to six divers for combat missions, or torpedoes and mines in external panniers. ''Special equipment'' for divers is carried in external pressurised compartments, located underneath the upper casing.
Published data suggests a length of 30.2m, beam of 4m and a diving depth of 200m. Maximum submerged speed is 6.5kn, while endurance is rated at ten days or 1,000 nautical miles. Main propulsion is a 160kw diesel generator and 1200kW/hr accumulator battery. No details have been released of any sales of these midgets to any export customer, but the shortage of hard currency and the low value of the rouble means that Russian export agencies can offer very competitive prices.
One of the largest operators of midget submarines is the Democratic People's Republic of Korea (DPRK). According to Jane's Fighting Ships no fewer than 55 76-tonne midgets have been built by the Yukdaesori shipyard in the last 30 years. Several have been used to land saboteurs and agents behind the lines in South Korea, and at least one has been captured by Republic of Korea (RoK) forces. Some are reported to be armed with two torpedoes.
The RoK Navy has not duplicated the DPRK's investment in midgets, but owns three, presumably as a means of assessing the efficiency of countermeasures. The KSS-1 type Tolgorae was delivered ten years ago, and another three Italian-built Cosmos type are used to transport Marine Corps combat swimmers.
Under the spur of ideological conflict with the West and war with Iraq, the Islamic Republic of Iran developed its own resources to defend the gains of the 1979 revolution. One of the fruits of this process was the construction of a midget at Bandar Abbas, using concepts derived from Second World War German and Japanese designs, and some imported materials. The prototype was completed in 1987 but needed major modifications to cure its inherent faults. Two more midgets were built to a North Korean design, but neither of these was considered to be an unqualified success. Reports suggest that work is continuing, and with the end of the war against Iraq and Western hostility shifting to Iraq, it is now easier to obtain. Although the Italian Navy pioneered the use of human torpedoes (known today as swimmer delivery vehicles or SDVs) and prompted the Royal Navy to develop its own ''Chariots'', in today's Italian Navy there are no midgets. However Cosmos of Livorno has sold a number of midgets abroad. The SX 404 type sold to Pakistan 20 years ago have since been replaced by three modern SX 756 type, displacing 40 tonnes and capable of diving to a depth of 100m. They can carry six swimmers and two SDVs, as well as 2 tonnes of explosives. Two very similar midgets were bought by Colombia.
Another Italian development is Maritalia's toroidal design, in which the hull is made up of transverse tubular sections or toroids. Although Fincantieri took up Maritalia's design with a view to developing a 300-tonne operational model interest appears to have lapsed in the project, presumably because no customer has been prepared to fund development.
Although some of the bigger midgets are armed with torpedoes, the fire control requirements of modern torpedoes are not suited to very small dimensions. The traditional use of midgets is to deliver very heavy (up to 250kg) charges alongside the hull of the target, or to enable swimmers to put much smaller limpet mines on vulnerable parts of the underwater hull, typically rudders and propellers. These charges are constrained in effectiveness by the need to be small enough to be carried by a swimmer. Modern compact explosives and shaped charges can only do so much; limpet mines can disable, but they are unlikely to sink a major operational warship manned by a crew trained in damage control.
The midget submarine continues to be admirably cost-effective for clandestine operations, but it has proved singularly ineffective as a means of exercising sea control or sea denial. Because it is primarily a means of transporting human operators to the enemy's ''doorstep'' it suffers all the limitations of those human operators. No amount of automation can make good the mental and physical strain of lengthy passages, which is why so many midgets are designed to be transported by ''normal'' submarines. Unless an enemy anchorage is very near - across an estuary, for example, an open sea passage is very hazardous and the operators will not be fit for operations at the end of that passage. The analogy is with strike aircraft, which can in theory refuel in flight to extend range almost indefinitely, but cannot then undertake the rigours of combat.
We can expect to see more midgets built, but they will only prove cost-effective when the conditions are ideal.
They have proved their worth in the past by inflicting pinprick damage on invasion fleets, and can prove very difficult to counter, as in the case of the Swedish intrusions. On the other hand, despite the claims made for them by their supporters, they have never proved decisive.