The Caspian Sea, long a Russian lake, is now witnessing a naval arms race. Before the Soviet Union broke up in 1991, the only nations bordering the Caspian were Russia (with most of the coastline) and Iran. But now those two nations have been joined by parts of the Soviet Union that have become independent states (Kazakhstan, Azerbaijan, and Turkmenistan). It goes downhill from there.
Iran shares a land border with Azerbaijan and has a historical claim on Azerbaijan. In the 19th century Azerbaijan (as in the area occupied by the Azeris, a Turkic people) was divided by Russia and Iran. Currently, about a quarter of the Iranian population is Azeri, but the Azeris of Azerbaijan believe all Azeris should be part of an independent Azerbaijan. This was how it was for centuries before Turkey, Russia, and Iran began seeking to conquer Azerbaijan. Some Iranian Azeris like this idea and Iran is always looking for ways to make Azerbaijan back off. So Iran is building up its Caspian naval forces, which is annoying Russia more than Azerbaijan.
The Iranian buildup includes a new corvette, an Iranian built 1,400 ton ship. Azerbaijan responded by buying $1.6 billion worth of weapons from Israel (which angered Iran a great deal). Among the items ordered were Gabriel anti-ship missiles. These are 522 kg (1,150 pound) weapons with a range of 36 kilometers. Azerbaijan will use these to protect its Caspian Sea coast from the growing number of Iranian warships being introduced in the area. Most of the Iranian Caspian “fleet” consists of small patrol boats. Some are armed with anti-ship missiles but they are basically coast guard type craft.
What really controls the Caspian is aircraft and Russia has the most of those. Russia also has the only water link to the ocean and thus the ability to bring in more warships on short notice. These, plus Russia’s larger air force, gives Russia the edge.
This is not enough for the nations that used to be part of the Soviet Union (and are still on good terms with Russia). That’s because Iran has threatened all of its neighbors on the Caspian and has claims on offshore oil fields that belong to Azerbaijan. There’s believed to be another 40 billion barrels of oil under the Caspian, and Iran wants to grab all it can. This makes all the other Caspian nations just a wee bit nervous.
The Caspian Sea is the world's largest lake and it is huge, at 371,000 square kilometers (about the same size as Poland). It is about a thousand kilometers long and 430 kilometers wide. It's saline but is only about a third as salty as ocean water. The Caspian has a 7,000 kilometer long coastline, with the largest chunk (1,900 kilometers) belonging to Kazakhstan.
Since 1952, a canal, linking the Don and Volga rivers, gave the Caspian Sea access to the Black Sea and the world's oceans. However, the largest ships that can use the canal must be no more than 140 meters (434 feet) long, 17 meters (52 feet) wide, and a draft of no more than 3.5 meters (10.8 feet). The canal moves over 12 million tons of cargo a year. About half of that was oil or oil products. The main reason for buying the new warships is to protect the offshore oil facilities and the movement of oil cargoes.
Since the 19th century a Russian (and later Soviet) flotilla was the largest naval force in the Caspian. After the Soviet Union dissolved in 1991, Kazakhstan, Azerbaijan, and Turkmenistan inherited most of that. Although all Caspian nations have, sort of, pledged not to get involved in a naval arms race. Iran has broken that arrangement and everyone else responded by bringing more warships into the Caspian. Russia and its three allies have an advantage because they can buy from anywhere and bring the ships in via the Canal. Iran has to build larger ships in the Caspian Sea yards. Smaller ships, and subs, can be brought in via train, which is what Iran is doing.