The UK’s Ministry of Defence (MOD) (including the British Army,  Royal Air Force, and Royal Navy) operate a variety of social media accounts:

As of September 2018, there were a total of 720 registered social media accounts:

• Facebook: 472.
• Twitter: 240.
• YouTube: 8.

It is important to note that the above are in constant flux, meaning the closure of old, redundant accounts and the opening of new organisation accounts will change the number.

Reference

FOI Request FOI2018/11321 dated 28 September 2018.