Before Russia annexed Crimea in 2014, the presence of Russian military forces there was strictly defined by a 1997 treaty with Ukraine 1997. The specified that no more than 25,000 Russian military personnel could be present on the peninsula, and only 2,000 of them could be air force and another 2,000 could be marines. Equipment limits also applied. The Russians could have no more than 24 artillery (guns or howitzers of more than 100mm caliber), no more than 142 armored vehicles and 22 military aircraft. Even naval forces, the main reason for Russian presence in Crimea, were also limited. Russia could only base the specific vessels (including tugs and other unarmed support ships) in Crimea. Even the pro-Russian Yanukovych government (ousted in early 2014) did not change the 1997 treaty extended the naval base lease to 2042. Ukraine was being well compensated for that lease through a Russian gas discount, amounting to about $4 billion a year.
Since the March 2014 annexation of Crimea by Russia, many things have changed on the peninsula. The first thing Russia has done after this action was to break the abovementioned treaty, lifting all limits on Russian presence in Crimea, and effectively take over the local Ukrainian law enforcement and military forces stationed on the peninsula.
All the Ukrainian military and law enforcement personnel was given three options - join equivalent Russian forces while keeping their rank, retire, or leave Crimea and continue to serve Ukraine. Only about 3,000 of 19,000 of the Ukrainian security personnel took the third option. Many of the soldiers and police in Crimea were ethnic Russians and didn’t mind the change. For the ethnic Ukrainians leaving Crimea would constitute hardship, as it would involve moving their whole families, and losing their real estate in Crimea. Overall, between 70% and 80% of the security personnel took the first option and switched their allegiance to Russia.
At first Russia announced it would return the captured equipment, supplies, and vehicles to Ukraine, and has returned some of it. However that process stopped on 15th April, and some of the unreturned equipment was given to the pro-Russian rebels in eastern Ukraine instead. That did not include any naval vessels and 43 of 72 Ukrainian ships were returned to Ukraine. Even though most Ukrainian security personnel remained the organizations they belonged to were usually disbanded or reorganized. In some cases units were unchanged but assigned to another command and changing their names. All this took a ew months. Then things changed a lot more as Russia began to greatly expand its military presence in the Crimean Peninsula. It was announced that at least 30 more Russian warships will be moved to Crimea by the end of the decade. This includes six Admiral Grigorovich class frigates, a Slava class cruiser, three Kashin class destroyers, two Kilo class submarines, six Buyan class corvettes, and six each of Project 22160 and 21980 patrol boats. Many of these ships are new and some are still under construction.
The Russian airpower in Crimea is also being increased. There are over 24 airfields on the peninsula, built there during the Cold War, and after it has ended only 5 of them were in use - two by Ukraine and three by Russia. Three of the old airfields are being reactivated since the Russian takeover.
Aircraft meant to be based in Crimea, at least 200 of them, include Be-12 and Be-200 flying boats, Ka-27 and Mi-8 helicopters, Su-24 attack and Su-24MP recon jets, Su-27 and Su-30 multirole fighters, Su-25 close air support planes, Orlan-10 UAVs, and last but not least, Tu-22M strategic bombers capable of carrying nuclear weapons.
Russian land forces located in Crimea now include two former Ukrainian marine battalions, an artillery group equipped with MSTA-B towed howitzers, coast defense brigade, and various air defense systems, notably S-300 long range missile launchers and a well-developed supporting radar network. Additions include more personnel and equipment, including Tornado artillery systems, Khrizantema-S guided anti-tank missile carriers, Bastion and Bal anti-ship missile launchers, and additional S-300 anti-aircraft missile launchers and radars.
Within Crimea Russia has also captured many Soviet era training facilities, most notable of them being a combat dolphin training center, and a carrier pilot training facility containing a replica of a Kuznetsov class carrier’s flight deck, including a ski jump ramp, catapult, and braking systems. These are expected to be back in business soon.
Russia's motivation for such a large presence in Crimea is mostly meant to cement its claim to the peninsula, reinforce its naval domination of the Black Sea, and discourage Ukraine and NATO from any future attempts to take it back by force. --Adam Szczepanik