Russia has shipped the first regimental sets of it advanced S-400 Triumf missile defense systems to China as part of a 2014 government-to-government contract, according to Russian military-diplomatic officials.

“Two vessels have delivered the first regimental set of S-400s from the port of Ust-Lug, Leningrad region, to China within the time limit established by the contract,” one source told Russia's TASS new agency on Tuesday. “It includes a command post, radar stations, launching stations, energy equipment [sic] and other property.”

A third shipment of the missile system was apparently damaged in the process and has been returned to Russia.

According to the Federal Service for Military-Technical Cooperation, the mishap occurred after a storm in the English Channel in January, when Russia began shipping equipment necessary to operate the missile systems.

“The work continues, and the missing equipment is expected to be delivered to the customer in the summer,” the source added.

In 2014, China ordered four to six Russian-made S-400 regimental units for an estimated price of around $3 billion. Head of Russia’s Rostec State Corporation Sergei Chemezov said in 2016 that there would be no shipment before 2018.

Moscow trained a group of Chinese military personnel to operate the S-400 system last year.

It is not yet clear how many S-400 units China is bound to receive or what type of missiles Russia has sold to China under the contract.

The standard S-400 battery consists of four transporter erector launchers (TELs), four launch tubes per TEL, in addition to target acquisition and engagement (fire control) radar systems and a command post, according to the Diplomat.

A battery can consist of up to 12 TELs if there is an additional fire control radar system in place. Each S-400 battalion is made up of two batteries and two battalions form and S-400 regiment.

This means China may have purchased anywhere between 60 to 200 TELs complete with the missiles and other equipment.

It took Russian Presidential Aide on Military Cooperation Vladimir Kozhin until November 2015 to confirm the contract. The contract made China the first foreign purchaser of the cutting-edge air defense system, followed by Turkey as the second buyer.

Chemezov has also revealed that Russia had not agreed to transfer technology or authorize licensed production.

That means the contract with China is different with the one Russia has struck with Turkey, which includes both technology transfer and domestic production.

The S-400 Triumf (with the NATO codename Growler) entered service in 2007 and is considered Russia's most advanced long-range anti-aircraft missile system.

Capable of engaging targets at a distance of 400 km and at an altitude of up to 30 km, the missile system can destroy aircraft, cruise and ballistic missiles. It can also be used against land-based targets.