A possible French Missile test over the Gulf of Biscaye on April 10-11 [UPDATED]

click map to enlargeAn odd Navigational Warning has appeared, for “space debris” along a 420-km trackline over the Gulf of Biscaye, from a point some 37 km southwest of Concarneau on the southern coast of Bretagne to a point some 20 km west of the French missile test base DGA Essais de Missiles near Biscarosse, southwest France. The Navigational Warning is for April 10 and 11, 2024, from 10:00 to 14:30 UTC (12:00 to 16:30 CEST).I do not think this Navigational Warning is really about “space debris”, but rather believe some sort of missile test is concerned. The southern end of the 420 km trackline being close to the French missile testing base at Biscarosse, while the northern end is in the area that the French Navy uses to test-launch SLBM’s, is a giveaway that it rather concerns some kind of missile. Also, a controlled reentry of “space debris” so close to the French coast would be very odd. So I do not believe for a second that the Warning truely is for “space debris”This is the text of the Navigational Warning: 051439Z APR 24HYDROLANT 716/24(37).BAY OF BISCAY.FRANCE.DNC 08.1. HAZARDOUS OPERATIONS, SPACE DEBRIS   101000Z TO 101430Z, ALTERNATE 111000Z TO 111430Z   ALONG TRACKLINE JOINING    47-36.00N 004-13.00W, 44-20.00N 001-30.00W.2. CANCEL THIS MSG 111530Z APR 24.Because the trackline starts in the area that the French use for SLBM test launches, and because “space debris” would perhaps indicate something with a high apogee, my initial thought (see also the title of the map above) was that it might concern a test of a new SLBM stage (it is definitely not a full M51 SLBM test, the range is much too short for that and those tests fire westwards).However, the 420 km length of the indicated track line, would also match two medium-range to long-range cruise-missiles of the French armed forces: the ASMP-A, which is airlaunched and meant to deliver a nuclear warhead; and the French-British SCALP-EG, also known as Storm Shadow, which is also air-launched and has a conventional warhead.If it concerns a ship- or submarine-launched cruise-missile instead, then the MdCN would also be an option, but that missile would have a 2-3 times as large range (edit: but see below).Calling a cruise-missile “space debris” is a stretch however. So many open questions remain as to the character of the missile in question. UPDATE 19 Apr 2024:The test happened on April 18 (the Navigational Warning was re-issued twice, for April 17 and 18). The French Ministry of Defense announced that it concerned a double launch of the Missile de Croisière Naval (MdCN) Naval cruise missile, one launched from the Frigate Aquitaine, the other from a nuclear  submarine in the Suffren class. The target was on land at DGA Essais de Missiles near Biscarosse.