[Fidd]

44. "Direction-finding"

Throughout the war, there was a multi-pronged attempt to locate both Uboats and RN ships through the use of directing-finding "or D-effing". Of the two sides, the allies had the advantage, as the geography of territory held (including Iceland) permitted better cross-bearings to be made of transmitting axis uboats and surface ships. However, at range, this of little use beyond that of "there are now thought to be 13 u-boats in your area" variety. This obscures the tactical advantages of shorter range D-effing, especially in the period before radar was common, and when done at ranges of 50nm or less, it allowed escorts to be detached to chase down a given bearing at speed, forcing the u-boat shadowing the convoy, even beyond visual range of the u-boat, forcing it down where it could neither communicate and might - with a little luck - also be sunk. Such attempts were much more successful when the Hunter-killer groups did so, as there was little scope for the u-boat being able to get away, and attacks were prosecuted until it was compelled to surface, or was sunk.

So how should this shorter-ranged "D-effing" work in terms of the game?

For U-boats, their ability to DF allied radio signals would give some indication of the bearing of a convoy, beyond that of hydrophones, and does so passively. It would allow for the position of a convoy to be established from a more imprecise BDU guestimate, allowing the u-boat to eventually establish hydrophone contacts later. This would allow for the game to allow a starting position for u-boats outside of hydrophone range, giving some much-needed content for navigators and radio-operators, who would need to decrypt BDU signals, move to the right area so directed, then D-eff, then plot an intercept course until one boat of the flotilla is in hydrophone and/or visual contact.

Conversely, allied shorter-range D-effing allows for the faster-moving escorts, fuel permitting, to be detached along a bearing to force a u-boat down, whilst perhaps summoning other assets to keep it down or kill it. The more frequent the German (or allied) radio-signals, and the longer, the more chance of a D-effing station (or ship/u-boat) being on the correct frequency to d-eff it in real time. Although both sides employed frequency schedules to complicate this for would be listers, and both sides used radio-silence as required, once the position of the convoy was known, this was of less and less utility.

In conclusion, for the Uboat d-effing a convoy gives some positional or directional information, and also some indication of it's escort size and composition. For the allies, it permits escorts to be employed more proactively (either at human direction) so that u-boats too often, or too long on the radio, are more likely to see a fast moving escort on the horizon heading more or less straight towards 'em.

Personally, I'd very much like to see this aspect of the electronic-war modelled, ideally with allied players managing assets within the convoy defence to not just react to boats within torpedo range of the convoy, but to keep them at bay, providing a more varied and difficult game experience for all concerned. Thought to be slated for development