The service remembers the four men who died and the two survivors
A village is holding a memorial service to mark the 65th anniversary of an RAF Wellington bomber crashing into the river, killing four crew members.
The crew were on a training night flight over the Irish Sea when they had engine trouble and ditched into the Teifi near Cenarth, Ceredigion.
Local historian Graham Elliott, BEM, researched many of the details and is in contact with the two survivors.
He said: "It's important not to lose sight of the feats of these people."
Service organisation standards will be displayed as a wreath is laid at the village's war memorial after the church service.
It marks the moment Wellington Bomber X-Xray No. JA453 of 83 Operational Training Unit crashed in Cenarth at 23.50 hrs on 23 August 1944.
The two survivors, Sgt Howard Hawkins, from Shropshire, and Sgt John (Jonnie) Robertshaw, from Hampshire, are now in their 80s and were not well enough to attend.
Jonnie Robertshaw and Howard Hawkins are too ill to attend
But they were present when the crash was first commemorated at the village, near Newscastle Emlyn, at the 50th anniversary in 1994.
Mr Elliott, a retired gift shop owner, said the crew were making for nearby Aberporth when they were forced to put down in the river.
He said: "In this time of continuing troubles for our servicemen, we believe it is right to remember those from the past who have "done their bit"."
"They were far away from the normal theatre of war, but they were killed. It's important not to lose sight of the feats that these people whose deeds were unrecognised.
"In those days, news blackouts were paramount, so there were very few people who got to hear about it. It wasn't reported in newspapers, it was just word-of-mouth."
Mr Elliott said interest in the tragedy was renewed several years ago when Sgt Howard Hawkins, from Shropshire, the rear gunner in the Wellington and one of the two survivors, a signed visitors' book of the then Fishing Museum at the north end of Cenarth Bridge.
In 1994, he and fellow survivor, radio operator Sgt John (Jonnie) Robertshaw, from Hampshire, attended a memorial with the relatives of the crew members who were either killed outright in the crash or in the subsequent fire.
Mr Elliott said: "They were both lucky. The rear gunner was in one of those capsules that you could open up. He could get out.
"The radio operator only got out from a hole in the fuselage when the wings was torn back."
He added: "In this case, D-Day had occurred, and it was thought that the end of WW2 was in sight.
"With the exception of the pilot and navigator, this ill-fated aircraft was being manned mainly by men who had been teenagers at the outbreak of the war, and were now able to "do their bit" for the war effort."