Source: Historical Section, COMNAVEU. "Administrative History of U.S. Naval Forces in Europe, 1940-1946." vol. 5. (London, 1946): 301-337 [This manuscript, identified as United States Naval Administrative History of World War II #147-E, is located in the Navy Department Library's Rare Book Room.]

PART III
The Assault Movement of NEPTUNE Forces

A. General Outline of the Movement

45. The NEPTUNE assault forces began putting to sea on the new time table during the morning hours of June 5th. By evening of that day the vast concourse of ships and craft were proceeding in accordance with the appointed program of movement toward the Beaches of Normandy. The general scheme of NEPTUNE movements, as shown in the accompanying sketch, may be summarized as follows.¹

    1. The U.S. assault force "U", carrying elements of the VII U.S. Army Corps (two regiments of the 4th division), was loaded at Torquay, Brixham, Dartmouth and Plymouth, assembled in Torbay, Brixham, Dartmouth and Salcombe and was routed via the British coastal channels, cross Channel route "C" ² swept channels 1 and 2, to the "U" assault area.

    2. The U.S. assault force "O", carrying elements of the V U.S. Army Corps (two regiments of the 1st division, and two of the 29th division) and certain U.S. Rangers, was loaded at Portland and Weymouth, assembled at Portland, Weymouth and Poole and was routed via the British coastal channels, channel "B", Area Z, cross Channel route "R", and swept channels 3 and 4, to the "O" assault area.

    3. 50th Division, was loaded at Southampton, assembled in Southhampton harbor and the Western Solent, and routed via channel "B".³

    4. R.N. assault force "J", carrying the 3rd Canadian division and certain British commands, was loaded at Southampton and Portsmouth, assembled in the Southampton harbor and the Western Solent, and routed via channel "F", area "Z" cross Channel route "U", swept channels 7 and 8, and thence to the "J" assault area.

5. The British assault force "S", carrying the 3rd British Division, was loaded at Portsmouth, Newhaven and Shoreham, assembled at Portsmouth, Spithead, Newhaven and Shoreham, routed via the British coastal channels, cross Channel route "J" and swept Channels 9 and 10, to the "S" assault area.

6. The U.S. follow up force "B", carrying the remaining regiments of the U.S. 1st and 29th divisions, was loaded at Falmouth and Plymouth, assembled at Falmouth, Fowey and Plymouth, and routed via British coastal channels, channel "C", and the American swept channels to the "O" and "U" areas, where it was to arrive by the second tide of D-day.

7. The British follow up force "L", carrying the British 22nd Armoured Brigades and other formations, was loaded at Tilbury and Felixtowe, assembled at Southend, Sheerness and Harwich, and sailed via the British coastal lanes, area "Z", the British cross Channel lanes, and thence to the British assault areas, to arrive on the second tide of D-day.

8. The first U.S. build-up convoy (EBP 1), carrying the preloaded U.S. division and supplies, was loaded and assembled in the Bristol Channel, sailed via the British coastal routes, channel "A", area "Z" and the U.S. cross the Channel routes to the "O" and "U" sectors, where it was to arrive by the second tide of D plus 1.

9. The first British build-up convoy (ECT 2), carrying the preloaded British division, was loaded and assembled in the Thames estuary, was sailed via the British coastal channels, area "Z", and the British cross Channel lanes, to the British assault area, which it was to reach on the second tide of D plus 1.

B. Composition and Timing of Convoys

46. The timing of NEPTUNE shipping movements was governed. by the army plan of battle. All sailings were scheduled so as to deliver personnel and cargo on the far shore, at the times and in the sequence required for the land

battle ¹ The timing of the cross Channel shipping movements was complicated by the fact that the vessels involved travelled at widely varying speeds. To standardize movements, initial convoys were designated as either slow (5 knots) or fast (12 knots). As each assault force required vessels of both speeds to accomplish its tasks, two convoys were formed for each purpose, both convoys of each "pair" being sailed so that they would arrive on the other side together and at the approprIate time.²
47. British and American forces followed somewhat different systems of assault movement. Before leaving English waters, British forces were formed into 16 or 18 convoys, or groups, corresponding to the assault formation which they would assume for the landings. Thus, each assault group (carrying a Brigade landing team) was sailed from England in two convoys (a slow end a fast) as a distinct group, and was not merged in convoy with the other assault groups of the same assault force.

48. The American Assault and follow Up Forces on the other hand, were formed into convoys, in accordance with scheduled times of arrival by tides. Both Force O and U merged

Assault Groups into the same two convoys for the cross Channel passage. On arrival in the assault area, the convoy formation was dissolved and ships proceeded to their assault group stations. Within each convoy, however, vessels were arranged in assault formation. Transition from convoy formation to the a assault formation was accomplished by having each assault group stop as the Convoy steamed passed its assault station.¹
49. British assault convoys were sailed so that only the leading brigades (regimental combat teams) would arrive in the assault area for H-hour. The supporting brigades of each division followed, in separate convoys close behind, in order to arrive in the assault area after the landing of the leading brigades had begun. All elements of the assault division were to be introduced, however, before the second tide of D-day. The follow-up force brought up a distinct new army division.

50. In the American sector the first two R.C.T. of each division were brought into the assault area at the same time. One initiated the attack while the other followed in over the same beach later on. The third R.C.T. of each division was not brought into the assault area until, the second tide of D-day. In fact the last regiments of the assaulting divisions comprised the bulk of the U.S. follow-up force. The American program for assault convoy movements therefore consisted of the sailing of comparatively few very large convoys, ² while the British program provided for sailing large numbers of comparatively small convoys.

51. The American forces had been assembled at a large number of small ports, and travelled primarily in large convoys. It was therefore necessary that they sortie from their various ports in convoy sections and rendezvous at sea. The British were able to form up each convoy in its entirety in the assembly areas.

52. The initial assaults were primarily infantry. But military vehicles, guns, and special equipment were required at a very early stage. The first convoys to arrive, therefore, carried chiefly personnel. Some military vehicles, guns and equipment were brought up in the earlier convoys, but the greater part was moved in by later convoys of each assault force. The accompanying sketches show the approximate position of convoys at H-hour, H - 6 and H plus 18.

C. Routing and Navigation

53. The general plan for routing. NEPTUNE convoys was:

    1. Convoys should move from their assembly anchorages, via the permanent swept channels of the British Coastal Routes, toward Area "Z".

    2. At an appropriate point, they were to turn out from the established channels and proceed to Area "Z", via routes specially laid out and searched for NEPTUNE (Channels A, B, F and K).

    3. At Area "Z", which was located a few miles off the British coast and due North of the assault area¹ convoys were to turn southward through an area of searched water known as the SPOUT.²

    4. On reaching the German mine barrier they were to pass into the assault area through ten narrow swept channels, (channels 1 to 10), which were subsequently widened until the entire SPOUT was cleared of mines.

54. The increase in the scale of NEPTUNE, from a three to a five divisional assault, required more room for the movement of the two new assault forces than was provided in area "Z". Two additional cross channel routes had therefore been laid out. (Routes C and V). NEPTUNE routes are laid out approximately to scale on the accompanying sketches.³

55. A reliable system of navigation was required to locate the swept channels in the proper place, and to make sure that the innumerable NEPTUNE vessels would follow their assigned courses. No special navigational methods were

required for the navigation of ships while in the British coastal channels. A few of the coastal navigation lights and radar beacons, however, were turned on for the occasion.¹ The special NEPTUNE routes were marked, at either end and down their center line, with distinctive buoys. The ten channels through the mine barrier were marked at either end, at the elbows and along the eastern edge, by a series of dan buoys. The transport areas were similarly marked.
56. In addition to the normal navigational methods, a number of electronic navigational aids were employed:

    1. On D minus 6, ten sonic underwater buoys were laid at the northern end of the 10 approach channels. These were laid sonically dead to come alive on D minus l. They would then be used by H.D.M.L's acting as marker buoys, to enable the minesweepers to start sweeping the approach channels in the correct positions.²

    2. All key buoys were equipped with special radar reflectors which gave a distinctive response on ships radar. Ships were thus able to take bearings whether they could see the buoys or not. With SG Radar installed in at least one out of every six LCI's and above, the reflector buoys provided a very great safeguard.

3. The majority of convoys were provided with special navigational leaders equipped with "QH" and "QM".¹ This enabled them to determine their position to a high degree of accuracy in any sort of weather.

4. Radar stations on the British shore maintained close watch on the channel area. The position of all ships and convoys were plotted on central plotting charts. C-in-C Portsmouth was thus able to discover at once if any ship or convoy was departing from its scheduled route, and to correct its position by a suitable radio message.

D. The Assault Forces Reach the Beaches

58. The entire vast program of assault movements proceeded basically according to schedule and along the established routes without serious deviation. Some mistakes, however, were made:

    1. Four groups of Force J, and one group of Force S, proceeded down channels to the westward of the correct ones. When this was discovered, before the groups reached the lowering positions, they cut across unswept waters to their proper positions. No casualties from mines were sustained, however, and all reached their appointed positions in time to assault as scheduled, except a few LCT of

Assault Group J-1.¹
2. The tail of convoy O.2 (which was a very long convoy) drifted eastward down wind and down tide, across unswept waters, and into channel 5, where Group G1 was pushed out. When the tide turned, the tail of convoy O.2 drifted off course the other way.²

3. Vessels of Convoy U 2 were likewise set to the westward by the strong tide and got into channel 3 where they disturbed the progress of convoy O.1.³
58. The waves of assaulting craft were aided, in finding the appointed beaches and the touching down at the right spot, by special devices in addition to normal navigational methods. Two X craft (small submarines) marked the approaches to beaches Sword and Juno. It was very important that Force S should not hit too far to the eastward. The coast in Force J's sector was not distinctive in outline. These craft, which sailed on the night of 2nd - 3rd June, being towed part way, were in position to mark the beaches for the original D-day (June 3th). When they received the postponement signal, they lay on the bottom all the ensuing day, and were able to mark the beaches accurately.

59. Certain MLs were designated navigational leaders, and fitted with Type 970 Radar. A projector was fitted to the PPI of this radar, from which a sort of lantern slide could throw an image on to the PPI scope. Predictions

were prepared which cast an image on the PPI scope exactly like that which the radar would show when the ship was located at a certain spot. When the radar image and the predicted image were matched the ship was known to be on the spot indicated. Predictions were made for points on the line of approach 5,000 yards and 1,500 yards (the line of departure) off shore. By use of these predictions, the navigational leaders brought the landing waves and control vessels to the intended line of departure with great accuracy.
60. The shoreward movement of assault craft was controlled by primary and secondary control vessels. These were PC's and SC's, in the case of U.S. Forces, and ML's and light destroyers, in the case of the British Forces. Control vessels were equipped, to find and mark the "line of departure" to beaches, so that the assaulting craft would be started shoreward in the right time, place and sequence.

61. Despite all of these preparations, however, both the primary and secondary control vessels on one battalion front of Force U became casualties. The U forces finally landed 1,000 to 1,500 yards south of their intended point. This proved a fortunate error, however, since both beach obstacles and land defenses were less formidable at the point of actual landings.

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Footnotes:

p.400 #1 The broad scheme was not always followed in detail. Exceptions which are noted elsewhere, were minor.

p.400 #2 The location of these channels are shown on sketch following.

p.402 #1 As has been seen in Chapter IV the broad outline of the time table for delivery of army units on the far shore was as follows: (1) Five divisions were to be delivered on to five selected beaches in the Bay of the Seine in the assault formation at, and shortly after, H-hour. (2) Two further divisions of follow-up troops were to be delivered on the second tide of D-day. (3) Two more divisions plus military cargo were to arrive on D-plus 1. (4) Thereafter army formations were to be delivered at the rate of 1.1/3rd divisions per day until a total strength of 30 divisions was reached. (5) After that, the build up was to proceed at the rate of three or four divisions per month as required.

p.402 #2 Each assault force was provided with two channels through the mine barrier, one for the slow convoys and one for the fast. The far end of the slow channel ran along beside the far end of the fast channel so that at the end of the run any pair of convoys was matched up side by side.

p.403 #1 The first group to stop had been placed at the rear of the convoy and so on.

p.403 #2 Convoy O 2 contained 293 vessels. (See NCWTF Report - in ANCXF Report Vol. III Page 96.

p.404 #1 Force U was loaded in 9 different ports and assembled over a stretch of coast line some 150 miles long. Force O was loaded and assembled at 3 ports.

p.405 #1 Area "Z" was a circle of 5 mile radius centered on a point 15 miles south of Rab light at position 50°25', 0°58' W.

p.405 #2 Four channels (channels R, S, T and U) were laid out across the SPOUT so that the convoys would not intercept one another.

p.405 #3 For the exact definition of Convoy Routes, see ON-17.

p.406 #1 ANCXF Report Vol.1, Page 43 Paragraph 82.

p.406 #2 ANCXF Report Vol.1, Page 42 Paragraph 67.

p.406 #3 See ANCXF (US) Report on Naval Communications in NEPTUNE, Page 29. See also Chapter V, Section for installation program on U.S. vessels.

p.407 #1 "QH" consists of three transmitters located at known positions, each transmitting a pip simultaneously. The difference in time which the pips from the two transmitters are received establish a line of points along which the receiving ship may be located. The difference in time at which another pair of pips is received establishes another line along which the receiving ship may be located. The point at which these two lines intersect, is the location of the ship. In the cross channel operation, "QH" was accurate to within 100 yards and "QM" which is a similar device was accurate to within 50 yards.

p.408 #1 Report of NC force J, and NC Force S.

p.408 #2 Report of NC force G.

p.408 #3 Report of CTF 124 (NC Porce U) Paragraph 10.