Pakistan is having AIP (air independent propulsion) added to its third Agosta 90B submarine. One of the Agostas was built with AIP, and the second has had it installed. AIP enables the sub to stay under longer, thus making the sub harder to find. AIP allows the sub to travel under water for 4-5 days at low speed (5-10 kilometers an hour).
Meanwhile, Pakistan is switching from France to Germany for its next batch of submarines, and is buying three Type 214 diesel electric submarines. Two years, Pakistan completed building the last of five Agosta subs, with the assistance of the French designers.
The 214s will be built in Pakistan, and the first one will be in service in about four years. The Type 214 is a 1,700 ton, 202 foot long boat, with a crew of 27. It has four torpedo tubes and a top submerged speed of 35 kilometers an hour. Maximum diving depth is over 1,200 feet. The Type 214 is similar to the earlier Type 209 and Type 212. The Type 214 also has a air-independent propulsion (AIP) system. This enables the sub to stay underwater for over a week at a time. Pakistan is paying about $350 million per sub.
The main undersea adversary for the 214s will be six French Scorpene class diesel-electric submarines being built in India. These are similar to the Agosta 90B subs that Pakistan has just finished building. The two designs are similar, with the Scorpene being more recent (and the result of cooperation between a French and a Spanish firm.) The Agosta is a 1,500 ton (surface displacement) diesel-electric sub with a 36 man crew and four 21 inch torpedo tubes (with 20 torpedoes and/or anti-ship missiles carried.) The Scorpene is a little heavier (1700 tons), has a smaller crew (32) and is a little faster. It has six 21 inch torpedo tubes, and carries 18 torpedoes and/or missiles. Both models are usually equipped with an AIP.
With both nations having these modern subs, they have very lethal weapons against surface warships. With well trained crews, 214s, Agostas and Scorpenes can get close to just about any surface ship, no matter how good the defenders anti-submarine defenses are. But it's the AIP boats that are the real killers. Without AIP, subs spend most of their time just below surface, using their diesel engines (via a snorkel device that breaks the surface to take in air, and get rid of the engine exhaust.) Snorkels can be spotted by modern maritime patrol aircraft, and both nations are getting more of these.
India is getting its first Scorpene in 2015, with one a year after that. Only the last three will have AIP. The price of the contract is quoted as $300 million for each boat. That could include AIP, because the boats are being built in Indian yards, which have much lower costs. European built AIP boats go for about half a billion dollars each. Typically, AIP adds about $100 million to the cost of a sub.