Most visiting cruisers never give submarines a thought, right up to the morning a low grey shape with no obvious bow wave appears off the beam and the mind takes a worrying few seconds to work out what it is looking at. France runs a serious navy, and a foreign yacht season here puts you in the same water as warships, fast patrol craft and, in a few specific places, submarines. None of it is dangerous if you understand a handful of facts. All of it can become dangerous if you assume a warship behaves like a merchant ship, because it does not.
The two coasts where it matters most
Naval traffic concentrates around the big bases. On the Mediterranean that means Toulon, which since 2011 has been France's largest defence base, home to more than 60 per cent of the navy's tonnage and the carrier Charles de Gaulle. On the Atlantic it means Brest, the second base, reached through the narrow goulet, with the Ile Longue submarine base on the southern shore of the rade. Ile Longue, open since 1972, is home to the four Triomphant-class ballistic-missile submarines that carry the French deterrent. I go into the local geography of both in my piece on naval activity around Brest and Toulon, but the behaviour rules below apply anywhere a warship turns up, which can be anywhere along the coast.
Why a submarine is a special problem
A submarine on the surface is the hardest large vessel to see and to read that you will ever meet. The hull sits low, often awash, with very little freeboard and almost no bow wave at moderate speed. Against a lumpy sea it disappears. Your eye is trained to find the white water of a ship's bow; a submarine gives you almost none of it.
It gets worse for the small-boat navigator. A surfaced submarine may not be transmitting anything useful on AIS, so the electronic safety net you rely on for merchant traffic can simply be absent. The radar return is small for the size of the vessel because there is so little above the waterline. In short, the one threat that is genuinely hard to detect is also the one most likely to be silent on your instruments.
When a submarine transits in or out of a base, it does not go alone. It moves inside an escorted security perimeter, with patrol craft and sometimes a helicopter, and that bubble is enforced. If you find yourself anywhere near it, the escorts will make their wishes known long before geometry becomes a problem. The right response is total compliance, immediately.
Warships under way: read them differently
A warship at sea is not bound by the same commercial logic as a container ship trying to make a tide. It may stop, reverse, launch a boat, conduct flying operations, or alter sharply for reasons you cannot see. Treat its movements as less predictable, not more, and give it room you would consider generous for a merchant vessel.
A few specifics worth carrying in your head:
- Warships frequently operate in company. Where there is one, look for two or three, plus a support vessel.
- During exercises a naval group may show restricted-in-ability-to-manoeuvre signals or display flag signals you will not recognise. When in doubt, keep well clear.
- Flying operations off a carrier or helicopter-capable ship create a moving keep-out zone. Stay out of it.
- A warship will often broadcast a securite call before a movement or exercise. Have VHF 16 live and actually listen.
Where they exercise, not just where they berth
The temptation is to think the navy only matters near Brest and Toulon. It does not. Both coasts carry charted military firing and exercise zones offshore, activated and deactivated by notice, where gunnery, missile trials and torpedo work happen. A submarine may dive and operate in these areas. The status changes day to day, so a charted zone tells you nothing about whether it is hot right now; you have to check the current notices and broadcasts. My separate guide to military firing zones off France covers how to find out before you cross one, and it is genuinely worth the five minutes during passage planning.
A morning that taught me the lesson
I learned the visibility point the hard way off the Cotentin one flat grey morning. I had two ships on AIS, both merchant, both comfortably clearing, and I was steering with one eye on the plotter and the other on the kettle. The crewmate on watch said, quite calmly, that there was something off the port bow that the screen did not know about. It took me a long ten seconds to resolve a low dark line into a surfaced submarine moving slowly, no AIS, almost no wake, with a small patrol craft shadowing it that I had also missed. We altered well clear, the patrol craft never had to say a word, and the lesson stuck: the plotter is a tool, not a lookout. Everything the navy does is built around the assumption that you are keeping a proper visual and radar watch, and on that morning a tired skipper nearly was not.
The collision-rules reality
Under the regulations a warship is a power-driven vessel like any other, and the give-way and stand-on rules apply. In the real world you do not stand on your rights against a naval vessel for the same reason you do not against a supertanker: the consequences land entirely on you. The professional small-boat approach is to make your intentions early and unmistakable. If you must cross ahead, do it decisively and at a sensible angle, the same discipline you would apply crossing the shipping lanes off Ushant and the Casquets or threading the Dover Strait traffic separation scheme for small craft. Predictability is the whole game.
Practical habits for the visiting yacht
- Keep VHF 16 monitored whenever you are within a few miles of a naval port or a charted exercise area, and respond at once if called.
- Do not rely on AIS to find a submarine or, in some cases, a warship. Use your eyes, your radar, and your common sense.
- Never anchor against or loiter near a buoyed military boundary. Those yellow special marks are there for a reason.
- If patrol craft or a warship directs you to alter or clear an area, comply immediately and completely. There is no negotiation and no upside to delay.
- Build the navy into your passage plan the way you build in tides and weather, not as an afterthought when grey appears on the horizon.
How this fits the wider traffic picture
Submarines and warships are the dramatic end of a spectrum of professional traffic you share French water with all season. At the merchant end sit the great streams of cargo ships funnelling through the western approaches and the Channel; in between sit fast ferries that throw a wake steep enough to roll you. The mental model that keeps you safe is the same across all of them. You are small, slow and manoeuvrable, and your one job is to be predictable and to keep clear. The navy simply adds the security perimeter, the silent submarine and the unpredictable exercise, three things a merchant captain never throws at you.
If you are planning a Channel passage that takes you past the western approaches, it is worth reading the naval pieces alongside the traffic ones. The same watchkeeping that gets you across the shipping lanes off Ushant and the Casquets is what spots a warship in good time, and the same calm radio discipline that works in the Dover Strait works when a French patrol craft calls you off Brest. Treat them as one skill, not several.
A calm word to finish
I have shared the water with French warships dozens of times and never had a moment's trouble, because the rules are simple and the navy has no interest in a yacht that behaves. The fear factor comes almost entirely from surprise: the visitor who has not thought about it, sees something low and grey and silent, and freezes. Take the surprise away by knowing the bases, the exercise zones and the one hard fact that a surfaced submarine may be nearly invisible to both your eyes and your instruments. Do that, and naval traffic becomes just another category of professional water-user to be respected and avoided, no more dramatic than a ferry on a schedule.
