Russia’s S-400 “Triumf” missile system is touted by many as the most advanced anti-aircraft platform on the planet. When equipped with its longest-range interceptors, the 40N6 missile, the S-400 is reportedly capable of engaging airborne targets as far as 250 miles away. It makes this system of particular interest to China, which is working to shore up its coastal defenses as a result of heightening tensions in the Pacific with the United States and its allies.

China signed a deal with Russia’s state-owned arms manufacturer, ROSTEC, to purchase the S-400 system back in 2015 but didn’t receive the first two platforms until April of last year. Now, reports are emerging that a shipment of those long-range 40N6 missiles destined for Chinese S-400 systems was lost at sea as a result of a storm.

“The contract was signed quite long ago. We were to supply [the 40N6 missiles,] but there was a failure,” said ROSTEC CEO Sergei Chemezov. “The vessel that was transporting those missiles–it was caught in a storm. So they have to liquidate all the missiles that were on the vessel and now we are manufacturing new ones.”

It certainly isn’t unheard of for container ships to lose cargo in rough seas. Still, the idea a shipment of advanced interceptor missiles would be as easy to lose in a storm as timber or other commercial goods falling overboard seems a little unusual. The fact that there have been no reports of Russian vessels losing such valuable cargo or of search operations being launched to locate such a shipment make the proverbial waters of this case even murkier.

Of course, if Russia did lose a shipment of 40N6 missiles somewhere in the Baltic Sea, it would certainly be of great interest to Western intelligence services (as The War Zone was the first to point out), offering a solid motive for keeping such an embarrassing gaffe under wraps. The fact that Russian and Chinese news outlets are controlled by their governments would make such a cover-up even more feasible.

If that is the case, the waters beneath the surface of the Baltic Sea may have seen a frenzy of submarine activity in recent months, as both Russian and American subs attempt to locate such a lost shipment. That, or ROSTEC may simply be making excuses for failing to deliver the goods to China as promised.