Huge explosions rocked a Russian airfield in occupied Ukraine on August 9, in Moscow’s biggest loss of military aircraft in a single day since World War II, but what caused them?

Saki air base, is currently the Crimean home to the 43rd Russian Independent Naval Attack Aviation Regiment (43 OMShAP). Su-24 bombers and Su-30 Flankers operate from the base and around 10 were destroyed during the explosions. What is currently unknown is what caused the explosions, with no official comment yet released from the Ukrainian MoD. We asked Justin Bronk Senior Research Fellow for Airpower and Military Technology at the Royal United Services Institute (RUSI) for his opinion on the likely cause: “Well, what I’m pretty confident about at this stage is that the three large fireball explosions that people are fixating on were not warhead impacts (which have a very different blast shape if you know what to look for), but instead were secondary explosions caused by stored Russian bombs and rockets detonating. The big blasts happen in the middle of what was clearly an already well-established fire – probably aviation fuel. That fire may well have been triggered by Ukrainian special forces using demo charges or munitions dropped from small UAVs, or loitering munitions. Either way, the initial fire spread and caused a chain reaction due to sloppy Russian ammunition storage practice – they were clearly keeping piles of bombs and rockets close to the aircraft as previously observed in Syria.”