Hunt for Red October was just on one of the freebie channels - lots of memories of St Mawgan (42 Sqn) flooding back.
In the late 1970’s, on Nimrod Mk 1 aircraft, things were rather basic, with Jezebel sonobuoys (passive only, no directional capability) & rather large (said to be the cost of a Mini car!) Mk 1C active & passive sonobuoys. The Jezebel sonobuoys could be set for shallow or deep, & with a couple of time settings - you didn’t want the associated radio channels to be max’d out later on in a sortie if you had managed to pinpoint a submerged tgt, think there were about 30 channels?? They could be dropped from 2 pressurised containers from medium / higher altitude, or, via an un-pressurised 6(?) shot rotary device.
When closing in for an attack solution, you would drop a pattern of 3 x Mk1C active buoys (about a mile apart?) with a passive Mk1C (& normal sonobuoy) dropped jointly in the middle with the active one; these boys only had a one hr lifespan. The active Mk1C sent out a ping, waited a set time (10 secs??) for a returned ping bounce (which would give you a range), then rotated about 15 degs, ping again, etc. The passive version rotated (I think in also steps) to give a passive bearing. Distance from the active buoy or 2 maybe 3 distances fixes to calculate a point) + / or bearing from the passive = attack solution, run down the bearing if feasible & either attack on the fix, or hope to get a “MAD” mark (magnetic anomaly detection) from the big sting on the tail = attack with either Mk46 active or Mk44 passive torpedo (or the WE177A nuclear bomb).
There was also a bathythermograph buoy - this was often dropped at the beginning of a search in order to assess the sea temperature, & more importantly, if there was a thermocline; if a submarine was below the thermocline, & the sonobuoy microphone was above it, it would highly unlikely to detect an submarine noises. Some basic sound / water theory - in principle, sound can travel a long way in a straight under the sea in deep water - you needed to be able to have a prediction / assessment of the direct path (DP) range of your tgt. If it was say 10 miles, then you would space your 8 or so sonobuoys in la ine initially at about 18-20 miles, 90 degs to the expected mean line of advance (MLA). If the tgt transited between 2 buoys, you would get a “closest point of advance” (CPA) & use this to calculate probable direction; sounds picked up (& printed on the thermal-sensitive paper (it stank to high heaven!) would give a probable indication of speed. Then you would advance down the MLA track, & drop a 2 line pattern, with closer spacing with a slight overlap - contact on 2 - 3 sonobuoys will refine the track / speed.
For water areas that were warmer / shallower / saltier (such as the Mediterranean), the sound waves wouldn’t go in a straight line for easy DP detection. Typical DP range would be very short, less than 5 miles? The sound from a tgt would bend downwards, then curve back upwards, then down, then up, etc, etc. Think a lot of concentric circles - this “bounce” could be say every 10 miles repeated 8 - 10 times!! The width of the detection "ring"would vary depending on water conditions but could be perhaps 5 - 10 miles across. This posed a huge problem in monitoring sonobuoys & then isolating which one was picking up the submarine - but where?? If there was contact on 2 buoys, the inter-locking rings could be one of many! We had an USN exchange officer who was very surprised that us Brits didn’t have suitable monitoring plan - let me talk with a friend… A few days later, yes, we had a plan - for sonobuoy pattern, distances between buoys & monitoring schedule depending on the convergence ranges / zones. Incidentally, for the disappearance of the Malaysia Air MH370 aircraft in the Indian Ocean, it is very possible that the data recorder pinger was being heard under convergence conditions = impossible to pinpoint.
We did a week operating from Gibraltar, working with NATO ships & subs in a typical exercise. One tasking was to locate HMS Dreadnought (an old & comparatively noisy early generation nuclear attack sub - but still a lot quieter than Soviet boats). With the convergence zone conditions, the search condition were going to be radar / ESM / visual; Dreadnought was meant to stick up a mast every 30-40 mins & /or squirt her radar for about 10 secs. This meant that the sonics team were surplus to requirements = tea makers + visual lookouts in port & starboard beams. I was in the port beam, marvelling at the lovely blue water…when we went right over a submerged sub, travelling in our direction. Woo hoo!! “Mark, mark, submerged tgt, on our track!!” A retro-flare was fired - very clever device - it fired backwards as same forward speed of the aircraft = dropped right below.
Action Stations was called by the captain - we circled around, ran down the track towards the flare, we got a MAD mark - for cost savings, I think for each exercise sortie, we were only allowed to drop one active Mk1C & one passive (plus the normal Jezebel). As this was an exercise against one of our own subs, we also dropped 2 ASTIs - “Air to Submarine Tgt Indicators” - mini-depth charges. Successful “attack” - the order was given to close up the camera crew (me in the port beam still, open up the window) - as we came around the captain said “uh oh” as the same time that the AEO said we had received a radio call from Dreadnought - saying “Missed!”
I took some lovely pictures of a Russian Foxtrot Class diesel powered sub, including one of a crew member in the conning tower waving their fist!! Oh dear! No-one was aware that a Foxtrot had sneaked into the Med - especially Dreadnought. So, down to me, we bombed a Russian sub! However, the Jezebel buoy got perfect sound of them making an emergency blow for surfacing.
Equipment / capabilities / tactics / resources have changed markedly over the last 50+ yrs & what I can indicate from back then has been published in open-source documents. Sonobuoys are exceptionally sensitive / versatile compared to then & the analysing equipment on modern ASW is incredibly complex & probably 1000+ times more capable than the stream-driven stuff that I used. The ASV21 radar on the Nimrod Mk1 was literally a WW2 design! Round screen & lots of dots!
The basic concept was that a tgt of interest would be known to leave the Northern Fleet in Murmansk, transit around northern Norway & enter the Atlantic via the Iceland / Faroes Gap. Tracking would be conducted by the Norwegians, then the Brits, possibly the French & Spanish, then the Americans from Lajes. SOSUS might come into play for the Gap. Reverse order when the submarine was returned from deep Atlantic to base.
When I joined the Nimrod fleet, the tracking was always covert & the handover to the next aircraft / country was also covert - this involved dropping an arrow of sonobuoys which would hopefully become “hot” shortly after the new aircraft came on task. The direction / spacing of the arrow gave MLA & speed. At some stage, someone high up decided that the final handover between countries would be overt - in other words, hit the submarine with lots of sound!! See what thye will do.
The first few months, wow, this was a huge surprise to the Soviet submariners - they would go into full evasive speed / manoeuvres, with the associated noises (props, cavitation, nuclear reactor, generators, etc), being picked up / recorded. Captains & navs would try to plot the expected MLA & second-guess which sortie might be the one to bid for; we didn’t care if it was a launch at 2359 hrs, it might be worth it. However, there was always the faint possibility that there would be a “hold” on active drops as that normally meant that the Red sub had a Blue follower…
After a while, the Russians had obviously been briefed that in around a certain geographical area, e.g. when the Noggies handed over to the Brits, expect to be disturbed! No big changes carried out. Back to boring.
Happy days of the Cold War!