SL meaning in Military and Defence ?

Sea Launch was a multinational spacecraft launch company founded in 1995 that provided orbital launch services from 1999–2014. The company used a mobile maritime launch platform for equatorial launches of commercial payloads on specialized Zenit-3SL rockets from the former mobile/floating oil drilling rig renamed Odyssey.

By 2014, it had assembled and launched thirty-two rockets, with an additional three failures and one partial failure. All commercial payloads were communications satellites intended for geostationary transfer orbit with such customers as EchoStar, DirecTV, XM Satellite Radio, PanAmSat, and Thuraya.

The approach Sea Launch used was to assemble the launcher on a purpose-built ship Sea Launch Commander in Long Beach, California, USA. The assembled spacecraft was then positioned on top of the self-propelled Odyssey floating launch platform and moved to the equatorial Pacific Ocean for launch, with the Sea Launch Commander serving as command center.The sea-based launch system means the rockets can be fired from the optimal position on Earth's surface, considerably increasing payload capacity and reducing launch costs compared to land-based systems.

Sea Launch mothballed its ships and put operations on long-term hiatus in 2014, following the Russian military intervention in Ukraine. By 2015, discussions on disposition of company assets were underway, and the Sea Launch partners were in a court-administered dispute about unpaid expenses that Boeing claims it incurred.

In September 2016, S7 Group, owner of S7 Airlines, purchased the assets of Sea Launch. Launch services were to potentially be provided by S7 Sea Launch, a US subsidiary. However, after moving the two former Sea Launch ships from California to Vladivostok, the S7 Group chairman stated that the program was indefinitely suspended. As of 2020, a replacement for the Zenit launch vehicle, with its Ukrainian first stage, was expected to be years away.