Maybe you don't know that British landings of D-Day were possible thanks to help from two British X-Crafts and their crews. This fact is virtually unknown. They were the HMS X20 and HMS X23; they were midget submarines. They spent five days on seabed just yards from Nazi guns. They were the first vessels off the coast of Normandy on 6th June 1944. They guided the British forces towards the beaches. In case of disaster, those manning the two X-Craft were all equipped with falsified French identity papers that would hopefully allow them to get ashore undetected by the Germans, evade capture and link up with the French Resistance. The codename of this action was 'Operation Gmabit'.

HMS X20 and HMS X23 acted as lightships to help the D-Day invasion fleet land on the correct beaches, as part of the Combined Operations Pilotage Parties (COPP). They marked with navigation lights and flags, the extreme west and east limits of Sword Beach and Juno Beach, the easternmost British and Canadian invasion beaches. Casualties at Sword Beach were minimal when the sheer magnitude of the raid is taken into account.

[Via www.nmrn.org.uk]

Setting out on 2 June from Hayling Island, Hampshire, HMS X20 and HMS X23 arrived in position on 4 June and due to the delay caused by bad weather, remained in position until 4:30 a.m. on 6 June (D-Day). They first knew the landings had started when a huge fleet of bombers flew above them to bomb German positions along the coastline. Then they surfaced, erected the navigational aids, an 18-foot telescopic mast with a light shining to seaward, a radio beacon and echo sounder, tapping out a message for the minelayers approaching 'Sword' and 'Juno' beaches. The landing craft homed in on the lights that came from the two X-boats.

 Lieutenant Ken Hudspeth [Via]

HMS X20 was captained by Ken Hudspeth, an Australian submariner member of the Royal Australian Navy Volunteer Reserve (RANVR). In December 1943, Hudspeth's new boat, X20, was sent to Portsmouth and from there was used to transport covert Combined Operations Pilotage Parties to the Normandy coast in order to obtain detailed data of the sea-bed and to check on coastal fortifications. This operation gathered a great deal of information that proved invaluable in the planning for D-day and Hudspeth was rewarded with a bar to his DSC. Ahead of the actual landings, Hudspeth (once again operating in X20) was ordered back to Normandy, and with his X-craft positioned as a navigation beacon off Juno beach, was able to assist in guiding-in the main assault fleet. For his part in the invasion Lieutenant Ken Hudspeth was awarded a third Distinguished Service Cross.

Lieutenant George Honour [Via]

HMS X23 was captained by George Honour, a British submariner member of the Royal Navy Volunteer Reserve (RNVR). Each midget submarine had a crew of five men on board. The submariners were at some risk of damage due to friendly fire and to avoid this, Lieutenant George Honour the captain of HMS X23 flew a White Ensign of the size more normally used by capital ships. On 28 November 1944 - Temporary Lieutenant George Butler Honour, RNVR, was awarded the Distinguished Service Cross for gallantry, skill, determination and undaunted devotion to duty during the landings of Allied Forces on the coast of Normandy.

[Via]

Since 2011, the troops from the Combined Operations Pilotage and Reconnaissance Parties are honoured with a granite memorial donated by Prince Charles on Hayling Island, Hampshire, where they were based.

American troops who did not have the same kind of guidance failed to find the correct route, with tanks having to be released into water that was too deep.