It wasn’t the biggest bang of the war. But a sudden flash that briefly illuminated the Russian port of Novorossiysk on November 18 had a significance that went well beyond its blast radius.
The explosion is believed to have been caused by a Ukrainian uncrewed surface vehicle - maritime drones that are changing the balance of power in the Black Sea and could profoundly reshape the future of naval warfare.
Ukraine’s radio-controlled bomb boats' first publicised action was in the early hours of October 29, when more than half a dozen of them attacked Russia’s Black Sea fleet at Sevastopol.
Footage from on-board cameras released by the Ukrainians showed black metal vessels charging at high speed across a choppy grey sea as machine gun and cannon rounds raised white plumes around them.
The Russian ministry of defence said nine aerial drones and seven marine drones involved scored only “insignificant damage” against one ship - the minesweeper Ivan Golubets - and the protective boom at Yuzhnaya Bay.
Independent analysts say the frigate Admiral Makarov also appears to have been badly damaged, although it does not seem to have sunk.
But it is not sinkings that are the mark of success. It is that they have seriously spooked the Russian navy.
“It’s going to go down in history,” said H. I. Sutton, an independent defence analyst.
“It is not the first time it has been tried. But it is the first time it has been successful and it has happened at scale. It is very much what we can expect going forward. It would almost be unrealistic in a future conflict to not involve these,” he said.
The success of the drones lies not in the relatively modest damage they have so far inflicted, so much as the projection of threat.
The October 29 raid mostly targeted shipping outside the narrow entrance of Sevastopol bay, but at least one or two boats appear to have got inside - penetrating what should have been impregnable counter measures at the entrance to Russia's most strategically important harbour.
That alone is a major achievement. Sailing a drone boat into Novorossiysk, which was supposedly out of range of Ukrainian attacks, must be doubly alarming for the Russians.
“The Russians have completely changed their defensive posture in Sevastopol and Novorossiysk. They’ve increased the boom - the floating barriers across the harbour mouth and changed procedures to close them much more frequently. Every warship, even a powerful warship, that leaves Sevastopol is now escorted by fast craft,” said Mr Sutton.
Combined with a series of other threats, the drone strikes have helped to effectively confine the Russian surface fleet in the Black Sea to its harbours.
That helps secure critical shipping lanes out of Odessa and further diminishes the threat of shelling or amphibious assault of Ukraine’s unoccupied southwestern coastline.
Russia’s submarines, which Western navies say are much more effective and well run than its surface fleet, remain a threat.
But Moscow’s once undisputed dominance of the sea war is well and truly over.
Unmanned bomb ships are nothing new.
Even before Sir Francis Drake sent fireships against the Spanish Armada in 1588, admirals thought about ways to close with the enemy without risking their own crews.
Western navies - and the Royal and US navies in particular - have been thinking about fending off fast-moving small boats ever since an al-Qaeda suicide bomber on a speed boat attacked the USS Cole in 2000.
But a rapid development of technology since then has created a revolution.
Remote control is now good enough to dispense with kamikaze helmsmen, and falling costs mean drones can be made and deployed quickly and in large numbers - given a little improvisation and ingenuity.
The Ukrainian boats show strong signs of both.
Images released by the Ukrainian military - and a photograph from Russian sources of a boat that washed up on the Crimean coast two weeks before the Sevastopol raid - show a sharp-prowed, narrow-beam speed boat about 18 feet long.
Mr Sutton, the defence analyst, matched the engine system visible on the video to the petrol-driven water jet used on commercial jet skis produced by the Canadian firm Sea Doo - something readily available on the commercial market.
Towards the bow, a rotatable camera is affixed on a small tower. Towards the stern, another low tower contains what may be the communications array used for control - possibly a Starlink terminal.
Starlink, a satellite-based Internet provider owned by Elon Musk, has been used extensively by Ukrainian ground forces for secure communications in battle.
The only visible bits of military grade, non-commercial kit are two pressure detonators taken from the Soviet-designed FAB-500 aerial bomb.
They look no more sophisticated than the home-made torpedoes Humphrey Bogart fixed to the African Queen.
Further details - including who pilots the remote controlled boats and where from - remain a Ukrainian military secret.
Russia has accused Britain of involvement - a charge the Ministry of Defence denies.
The Ukrainian ministry of defence, which appealed for crowdfunding to build more, has put the price per unit at 10 million Ukrainian Hryvnia, or about £222,000.
Not cheap by civilian standards, but a very good price for taking out a multi-million dollar warship.
Both sides in the war make extensive use of drones in the air - from purpose built Bayraktars (favoured by Ukraine) and Orlan 10s (Russia’s main reconnaissance drone), to cheap Iranian-built Shahed 136 “kamikaze” devices and shop-bought quad-copters modified to drop hand grenades.
The sea is a slightly different proposition. Warships are simply too big and complex to feasibly become entirely unmanned, said Ali Kefford, a naval journalist.
Nonetheless, “drones are very much the way forward,” she said. “The Ukrainians are also very savvy with their maritime warfare. But that is where we are all going.”
Naval thinkers have been anticipating drone battles at sea for some years.
Houthi rebels in Yemen have used several unmanned boats guided by on-shore operators against the Saudi Navy and tanker shipping in the Red Sea in recent years.
The most enthusiastic adopter has been Iran, which Western governments believe has built hundreds of such craft in preparation for a possible showdown with the West.
“There was always the working assumption that if the Iranians deployed all their fast attack craft they would overwhelm everyone else in the gulf,” said Tom Sharpe, a retired Royal Navy officer who faced down Iranian boats when he commanded a frigate in the region.
“The Iranians would test reactions with their manned boats all the time. You’d see these craft, sometimes 10 or 15, coming at you traditionally as you go through the straits of Hormuz.
“You manoeuvre, they manoeuvre, you escalate your warning process - generally speaking you were not allowed to engage them. But that is what it is: They want to see how you behave.”
In the event, the first proper water drone clash has occurred in the Black Sea, not the Gulf. But the threats and opportunities they present are the same.
The drones’ advantage is in numbers: only one has to get through to score a hit, and it is incredibly difficult for even modern warships to respond to a dozen or more fast-moving threats simultaneously.
Mr Sharpe, the former frigate commander, described relentless exercises off the coast of Scotland facing “jet skis and multiple ribs coming at you at the same time” to test how to cope with such attacks on both lone ships and convoys.
The best protection for a fast warship like a frigate or a destroyer is either a rough sea, or sailing out of the drone’s operating range.
But in a confined space like Sevastopol harbour, or even a small sea like the Persian Gulf or the Black Sea, that is impossible.
In that case survival relies on a “layered defence” - a combination of early intelligence, helicopter overwatch, “then lots of fast automated weapons and aggressive manoeuvring to deal with the attack when it happens.”
Even then, “if you are not highly trained for it and have not practised recently, or you’re not paying attention, then you are in big trouble. By the time you see it, it is too late,” he said.
“If I was a Russian captain and I saw these things coming I would be very worried.”
Conventional navies - in particular the Royal, American and Chinese - have already been experimenting with their own uncrewed surface vehicle programs.
But most of those programs focus on reconnaissance and force protection.
Swarm attacks, says Mr Sutton, have generally been viewed as a threat to counter rather than an opportunity to exploit - possibly because of the association with suicide bombers.
That has now decisively changed.
Physically, financially, and politically, Ukraine’s remote-controlled bomb boats offer low risks and high returns.
Their arrival on the high seas could have profound consequences.