Dan Yr Ogof, The Battle of Britain Series

With no progress on the issues in Tucks Rift, Andrew and I decided to travel a bit further West to make use of the continued good weather in the Dan Yr Ogof cave system. The show cave is closed to tourists at this time of year but cavers are still allowed in, either through the locked cavers cat flap or down the chain to the resurgence. The shortest route into the Battle of Britain series is through an 18 m long sump at the back of the resurgence passage so down the chain we went.


Andrew lowered the gear from the balcony that overlooks the river on his very red rope. Once inside a mixture of walking traversing and wading for 140 m took us to the back of the cave.


The low temperature and the carry to the back of the cave had brought on Andrews snuffles so he chose not to dive as doing so would have risked damage to his ears. I kitted up in the water while Andrew tied off the line real on a dry ledge and took some pictures. Neither of us could remember exactly where the sump passage started but after a short search it was located to the North, directly below an above water keyhole passage.



With the vis limited to about half a meter I was glad to find the remains of the old line after reeling out about 10 m of new line. After tying the new line to the old at a belay I followed the old line to the airbell that mark the end of the sump. Flooded passage does continue on from below the airbell. The last reported person to look at it was Andrew several decades ago but that was not the objective for today. In the airbell the original hand line for the climb up and gear hanging was still in place. After an inspection of the latter the dive kit was stacked on a ledge, this looked to be safer than hanging it from the line which has not been treated well by time and flood water. With the top belay out of sight and and not available for inspection the 5 m rift was climbed with some trepidation. At the top the rope and belay look serviceable if not ideal. From the position above the sump pool a promising rumbling sound could be heard. The aim of the trip was to look at Gwyn Saunders Hall to see if there was an obvious collapse that could be blocking the water flow. This is one theory why the cave now reacts more quickly to rainfall in its catchment area. There are other theory’s which also need investigation.

From the top of the rift (which runs North South) the passage goes off to the North, soon dropping to a crawl before swinging round to the West and increasing in height. After only a couple of meters the floor falls away in shelves into a North South fault rift with a tube passage going off WSW. This is a fine walking sized tunnel with water flowing from the far end and running into a passage that goes to the South, dropping to create a sump. At the end of the main tunnel lies Gwyn Saunders Hall which runs NE to SW. From the survey the Hall is about 60 m long by 10 m wide. It has a vaulted ceiling formed in a fragile limestone layer. The water from the main cave (which sinks just beyond the end of the show cave, in Lakes One and Three) rises on the far side of the Hall in Lake Zero, from where it flows into the tunnel I reached and other sumps.

Naturally the above is completely different from how I remember the place from my one previous visit about 8 years ago. So much so that when I saw the roof of the main tunnel come down to meet the flowing stream water I thought something was wrong. I clearly remembered this point as a 2 m climb down. Because of this mistake I didn’t explore further, assuming I had missed the proper route into Gwyn Saunders Hall and returned to the top of the 5 m rift to search for the correct route on. Despite grovelling around in some high level passages no other route was found and I returned down the rift, kitted up and dived out.

Back in the resurgence cave Andrew had been poking about in a few places and had shifted his dive kit back out of the cave. Despite my long absence he didn’t complain and even claimed not to be cold. This was to change as we exited the cave at sunset, dodged the dinosaurs and shifted the kit back to the car where it promptly froze to the ground when we put it down. After a chat with Ashford, the cave owner, we trundled back to Andrew’s house discussing what had been found.


Later, when we were able to hunt out and consult the original survey of the Battle of Britain series in CDG News Letter 98:18 we had a different view of the water levels. What was found on the trip may have been normal. My lack of investigation where the roof came down to the stream way in the main tunnel just before Gwyn Saunders Hall now looks like big mistake, a return may be needed. Lets hope the weather holds.

Series - DYO Battle of Britain

  1. Dan Yr Ogof, The Battle of Britain Series
  2. DYO Battle of Britain rematch
  3. A sunny day for BoB
  4. BoB(ing) along

10 thoughts on “Dan Yr Ogof, The Battle of Britain Series”

  1. That (wasn’t) snow, it’s the sediment in the water that was making the vis so bad! 😉

    …look forward to the return trip and the proper exploration beyond where the roof drops down to the stream. Although, from the very few times I’ve been underground alone, I can understand just how scary it gets when you are not sure you’re in exactly the right spot… All those important questions that race through my mind. How long have I been here? Will I find the right way on? Can I find the way back? Will people (like my Mum) be worried where I am? Is there time left to get out and eat my Sunday roast?

  2. Excellent report Colin, I too was in Danny on Saturday.

    I had intended walking on the Black Mountain above Dan Yr Ogof on Saturday, but as I turned into the car park, I met a couple of cavers and was persuaded that carrying a drill and batteries through the cave would be much more fun than walking in the cold on the surface. Water levels were very low due to the freezing conditions, and we were only moist up to our waists through the lakes. A couple of hours were spent digging out spoil from the previous trip before drilling a series of holes and loading them with Dr Nobel’s special preparation. Alas we failed to hear the avalanche of boulders follow the two explosions, so can assume that the boulder choke is still to thwart our attempts to pass it.

    I have been building a interactive survey with cave passages loaded into Google Maps with photos of the cave embedded in the page. This is an older survey, so does not include the Battle of Britain Series, but does include a photo of Colin in a sump in the cave if you look hard enough!

    My Dan Yr Ogof interactive survey

      1. It is me who has been building the Google Maps of the area. Google have an open API for the maps so you can build and add a lot of controls to them, or add and develop exiting utilities. All very interesting stuff and is eating up a fair bit of my time on an evening.

        Links that you suggested have been added.

  3. Hi Brendan, thanks for your comments and also for the work you have put into the interactive survey. I have been looking at it for a few weeks and except for one photo it is very good 🙄 The BofB surveys that I have seen are in the CDG Welsh section sump index and the NL listed in the report. The sump index survey is more up to date. The NL survey offers a better depiction of the passage. There may also be a published survey in Descent at about the time of the first discovery of the series.

    We didn’t hear any rapid expansion digging techniques on Saturday; you will have to use more next time 😆

    PS: Look out when you write comments like the above, Pete will start hassling you for trip reports…

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