Actually, no. It was no enemy that we were after, but a pillbox hidden in the moss - the innocent sort for carrying medicines rather than the ugly sort used for holding the enemy at bay. But the drugs that this pillbox might once have carried had long since been supplanted by a rolled up visitors' book and a rubber stamp depicting a squirrel in lurid green. If I hadn't been with Pat I would never have dreamed that this anonymous grey cylinder was in fact a Dartmoor "letterbox".
There are roughly 2,000 of these quirky capsules hidden over the 365- square-mile moor at any one time, and every year some 10,000 'letterboxers' come from as far afield as America and Russia to hunt for them and, when they find them, take away impressions of the rubber stamps they contain as their trophy. In May, says Pat, she's helping to organise the visit of 150 French schoolchildren. They come every year, and they love it.
That day, however, there seemed to be just the two of us out in the intermittent sunshine of early spring. The morning's rain was sliding off the surface of the hill. Bad winter weather had kept most letterboxers indoors, although on a good weekend there could be up to 1,000 individuals on the moor, puzzling over clues and fossicking under hawthorns, rocks and standing stones. But even on the busiest of days, where letterboxers go they often never see another soul for hours. "Except occasionally the SAS", added Pat, "who ask us where they are".
There's no particular uniform, other than a compass, rucksack, stout boots and a slight air of eccentricity. And no real rules of engagement either. As we got our bearings for Foals Arishes, the second box of the day, Pat related how the activity's leading man once found a clue hanging on the wing-mirror of his car, in a carrier bag. "It told him that he'd have to put on a dress and skip through the woods singing "I believe in fairies" to find the box in question." And did he? Of course. The photos came through the post a couple of days later, but to this day he's never found out who set him up. "Ah," smiled Pat, "In those days Godfrey would do anything for a box." It must be something in the air.
The Godfrey in question is Godfrey Swinscow, now in his late 70s. It was he who revived an obscure pastime 20 years ago by founding the 100 Club for people who've collected the stamps of more than 100 boxes. But the beginnings of letterboxing date back far further, to 1854, when one James Perrott left a glass jar by a remote pool so that visitors could leave their calling cards to show they'd been there. Since then the numbers may have multiplied and the technology changed, but the principle remains the same.
This is how it works: letterboxers stomp over the moor to secrete their pillboxes (each containing a tailor-made stamp, a visitors' book, and the hider's contact number for any problems) in suitable crannies. Then they publish "clues" - usually compass bearings, together with a brief topographical description of the hiding place, viz "under a triangular rock 20 paces east of a willow clump" - either in the monthly newsletter, or in the biannual catalogue.
Then the hunters sally forth. Each letterboxer carries a distinctive calling-card stamp of their own - Pat's is a galleon called Quest, her husband's is Jude the obscure - and they leave their marks in the visitors' books of the boxes they find, at the same time as taking an impression of the resident stamp for their collection. They also sometimes leave items of post for the next finder to bring back to civilisation.
And if all that sounds fairly mad, that's because it is. Only the British would create a sort of fox-hunting without tears, combining the satisfaction of train spotting with the skills of orienteering. It costs practically nothing to do, but placates the primitive urge to hunt and gather, without, in the words of Godfrey Swinscow, "stealing any bird's eggs."
That's not to say that it is entirely legal. Letterboxers do not have the landowners' permission to hide things on their property, but they cause very little disturbance. Less so, perhaps, than the groups of ramblers who tramp from tor to tor.
After years of disapproval, the National Park Authority has this year given letterboxers tacit endorsement by publishing a leaflet which describes what letterboxing is and how to get started. This is a milestone in their mutual relationship, says Pat. "We're a pretty co-operative bunch. If there's a problem with a letterbox, it's usually removed within 24 hours." At the longest, a box could stay outdoors for five years. Regular meetings with the authority and the military ensure that the 'boxers react swiftly to requests to steer away from particular areas.
By now we're on our fourth box of the day, and although they've all been relatively close together, we've already been out for a couple of hours. I can see how it would be easy to do 10 or so miles in a day without being aware of it. Do letterboxers ever get lost? "The mist can be a problem," concedes Pat. "The locals call it being pixied. You have to take your coat off and turn it inside out for the pixies to leave you alone."
After that I hardly dare mention new technology, fearing that mention of the Internet, e-mail or mobile phones would be about as welcome on Dartmoor as an adder's bite (another occupational hazard). But I've underestimated Pat: "Oh yes," she says, "There's letterboxing on the Internet, and I've got a hand-held GPS" (a satellite-based navigation system). She even carries a mobile phone with her, and occasionally she's used it to berate or congratulate the letterboxer responsible for the box or clue she's hunting.
But such technological aids don't alter the fact that many letterboxers know the moor like the back of their hands, and are sometimes called on to help in search and rescue.
At the last letterbox of the day I write "Wish you were here" on a postcard to my children and stuff it back into its heathery hiding place. They would have enjoyed this treasure hunt.
It's not always such a solitary pursuit, says Pat, as we head for home. There are letterboxes in pubs, for when the weather's really bad, and not so long ago a group of disabled enthusiasts used to travel around in a van, sending out their driver to locate and bring back boxes close to the road.
Include added distractions such as the get-together every Wednesday in the Dolphin at Bovey Tracey, and all-day parties in Princetown on every clock's change, and it can become a sociable, time-consuming hobby. "You can tell dedicated letterboxers from the dilapidated state of their houses," grins Pat, "they have no time left for DIY." Pat herself not only has her own 40 boxes on the moor to administer, but is also learning German and studying for a history A-level, as well as doing a full-time job.
We reach the car, blessing the weather, which has resisted the temptation to turn us into drowned rats. The wet is a hazard in more ways than the obvious, reveals Pat. "It brings unexploded bombs to the surface". So I wasn't that off target in my flight of fancy about the bombing run after all...
Three days later my Wish-you-were-here postcard re-enters our lives via the boring old slot in the front door. An added stamp reading "Woodstock Wanderers" reveals whose hands had found it and carried it off the moor, but I tell my children that it has been delivered by the pixies. Poor papa, I can see them thinking. Far too much fresh air.
Most people get into letterboxing after bumping into someone behaving oddly on the moor, but this year, for the first time, complete details of who to contact are available in the new leaflet, Letterboxing, published by the Dartmoor National Park Authority, Parke, Haytor Road, Bovey Tracey, Newton Abbot (01626 832093). Alternatively, you can contact Pat Clatworthy direct (01392 832768).
Letterboxing is also practised, to a much lesser extent, in the Lake District, Brecon Beacons and the New Forest.
How to get there
Dartmoor is within a half-hour's drive of Exeter and Plymouth. Cross- moor bus services start from both cities (01752 222666 for further information).
Where to stay
The Plume of Feathers in Princetown is actually the oldest building on the moor (1795), as well as being a regular meeting point for letterboxers. Bar food for big eaters and B&B from pounds 15.50 ( 01822 890240). In a less wild location and with a rather more delicate menu, is the Church House Inn at Holne, near Ashburton. B&B pounds 19.50 to pounds 27.50 (01364 631208). If you want to stay for next to nothing, then unroll your sleeping bag on the floor of one of Dartmoor's camping barns. There's a particularly good one in Holne ( 01721 24420).