The following synopsis is from the British National Archives,
Kew (AIR 50/281/217) from the following “Report on Loss of Aircraft on Operations”

Time 20:06 16th September 1943. 8 Lancasters from 617 Squadron and 4 Lancaster Mk. III from 619 Squadron depart RAF Woodhall Spa and headed for Cannes in southern France.

They were instructed to destroy the coastal rail link between France and Italy by bombing the Antheor railway Viaduct. Each of the Lancasters carried 7 x 1,000 pound bombs.

Briefed Route: Selsey Bill - Cabourg - 47.35N 00.45E - 45.12N 05.42E - Cap Ferrat - Antheor Viaduct - St. Raphael - 46.30N 01.00E - 46.30N 02.30W - 46.15N 05.50W - Predannack.

The aircraft crossed the south coast of France at Cap Ferrat and circled the rendevous island until the squadron had assembled. E619 was due at the renndevous at 00.30 hours and the E.T.A. was 00.40 hours. 

EE106 overhead target. The aircraft was the last to bomb the target at 1.20 hours from 300 feet, the target being identified visually. A small amount of light flak was encountered but no damage was noticed at the time. Delayed action bombs were used and no results were observed.

Height was gained over the sea to 6,000 feet and the compass was checked (method not given). Course was set 288° to allow for an estimated 60 m.p.h. southerly wind. There is some possible confusion here, in the story as told as to whether courses were “True” or “Magnetic”. The Navigator says “True” while the pilot at first said “Magnetic” but they finally agreed that “True” was correct. The aircraft climbed to 12,000 feet for the homeward journey and entered cloud at 8,000-12,000 feet, flying in cloud continually until the descent was made later at the estimated position of the French coast. GEE was unserviceable and the navigation was all by dead reckoning. As the winds to the north has been westerly and lighter on the outward journey, course was altered to 295° between Long. 2° and 3°E. At the outward position by D.R. of 46.30N 01.08E course was altered to 270° at an estimated time of between 03.45 hours and 04.00 hours.

At the E.T.A. French coast (04.15 hours) they descended and broke cloud at 6,000 feet, expecting to cross the French coast. Instead they found themselves over a lighted town which they thought must be in Spain and it was realized for the first time they were off track. Course was altered to 330° for about 50 minutes and an M.F. fix was then asked for (approximately 05.05 hours). As Plympton was unable to plot they they were given a Q.T.E. of 200° from Plympton (05.30 hours). At this time they were still inland. The coast was crossed at 05.50 hours and an S.O.S. fix was asked for. No reply was received except letter “K” reported. It is noted here that the last was heard of E/619 by the home base was a fix at 05.55 hours, position [mutilated word] 43.N 06.17E which E/619 did not receive.

This represent an approximation of the estimated route
that was flown that night by the crew after the bombing run.

120 miles W.N.W. of Santander Spain. The upper sky cleared and they were able to get an Astrofix 120 miles W.N.W. of Santander. (Black plotting from this would indicate that the course to the lighted town may have been about 50° off the briefed route).

The Flight Engineer checked the petrol and it was found to be only sufficient to reach approximately 48° N. Latitude, near the Brest peninsula. The captain decided that, rather than be forced down in enemy waters, it was preferable to proceed in the direction of Gibralter, though he did not hope to reach it. As they had no map of Spain they followed round the coast about five miles off.

About 12 miles north of Operto Portugal (time approximately 07.00-07.15 hours), it was decided to land and, as there was a heavy ground haze over the land, it was considered preferable to come down on the sea. The electrical apparatus was destroyed (V.H.F., I.F.F., GEE and MONICA) and the aircraft was put down on the sea about 200 yards off shore. The crew took to the dinghy but were picked up and taken to shore by some Portugese fishermen.

The aircraft was washed ashore and some light flak damage holes were found in the port mainplane, probably from the Viaduct defences as the crew did not think they were fired vat over Spain. The crew were soon taken in charge by the authorities and removed, but as far as they are aware no attempt at salvage was made by the Portugese authorities and they presume that the aircraft was allowed to lie and be broken up by the sea.

The following scenario was received from the son of Lancaster captain and pilot Flt/Lieutenant S.E.J. Jones 

Recently I have had contact with the son of Flt/Lieutenant Jones and he relayed an account from his father that suggest there ws no navigation error on the return mission but they were "hit by flack from a flack ship just off the coast and Mickey Martin of 617 fame whom he knew well flew alongside to check the damage. He advised not trying to fly back 800+ miles over enemy territory but instead head to Spain."

"He escorted them to the Spanish border then waved goodbye and set off for home. Dad told the crew to jump but on being told he was ditching rather than jumping they elected to stay! A lively discussion then went on about the possible nasty reception they might get in pro Nazi Spain and they decided to fly on to Portugal our oldest ally. He had already ditched in the sea earlier in the war and so they put it down in the water off Porto. Again his recollection was putting the Lanc down and then the crew getting into the dingy. A fishing boat arrived and took them to Vila Do Conde"

 "in 1945 Flt/Lieutenant Jones joined BOAC then BEA and as an aside in 1956 flew the Queen to Lisbon and then Porto on her state visit. At Porto airport he was handed a letter written in Portuguese that turned out to be from the Captain of the fishing boat that had picked him up."

" Interestingly Flight Lieutenant Mickey Martin of "Dam Buster" SQN 617 was hit by flak when bombing the same Antheor railway viaduct later in the war and also unable to make it back but by then the Allies had taken Sardinia and so he landed there."

After a period of time the entire crew is repatriated to England from Portugal including Gordon (ED) Deschaine who is reassigned and continued to fly many more missions over Europe.  On May 25 1945 he was awarded the Distinguished Flying Cross.  "This Warrant Officer has completed numerous operations against the enemy in the course of which he has invariably displayed the utmost fortitude, courage and devotion to duty."

It's only recently his family has learned of this incredible story and his well deserved recognition.  Ed sadly passed away Sunday, April 16, 2017 in London, Ontario, Canada at the age of 95 years.

The DFC awarded to Ed Deschaine "This Warrant Officer has completed numerous operations against the enemy in the course of which he has invariably displayed the utmost fortitude, courage and devotion to duty."

A plaque commemorating the ditching and rescue was recently unvieled in the town of Vila Chã, Portugal remembering that fateful night in September 1943.

Ed Deschaine's log book entry with remarks "ditched Portugal"