Of course SH5 could be used, though i am more familiar with SH3 +GWX.
Lying (almost) still ahead of a convoy is a good idea, if you a) do not show your periscope and b) one of the leading escorts does not accidentally run over you.. risky business. Keep your bow in direction of the convoy's course for less exposition, from accidentally surfacing to ASDIC echo profile just in case, to engine noise.
Also this tactic depends on letting embed you in the upcoming convoy columns, then turn 90 degrees and calculate torpedo solutions. You do not need 90 percent angle, and the TDC is well able to calculate the shots beforehand, but 90 degrees and close is usually the best situation for any submarine attack.
Also when the convoy zig-zags with you ahead of it, you will have to do it all again.. unless you are very lucky.
In the convoy submerged, you would have to be very quick, since once near/in the convoy with the escorts past you, you HAVE to use the periscope. No problem at night and in any but calm seas, but you have to have good situational awareness of those hulks steaming all around you.
Ahead of a convoy it is of not much use to lie at a greater depth than PD though, because ASDIC will most probably detect you from 30 meters on, also you need time to get up at PD and find your targets.
The classic tactics in early war was to just go in from behind at night surfaced, evading the escorts, and patiently pick your targets, maybe even attack with the deck gun. You can outrun any corvette surfaced, and you will usually know the convoy's general course from watching some time before. Wait for a zig or a zag until the cloumns have gone into formation again, then strike.
ASDIC is pretty useless against surfaced boats and most escorts did not have radar in the early war, the merchants will also shield you from visual or radar detection, no hydrophone will hear you among the merchants' screws, and no one will see you below the horizon at 5-7 knots from the ships's side, running in mid of the rows with the merchants.
Or the real classic tactic is outrunning the convoy with the "Hundekurve" just out of detection range (visual or radar), +- parallel to the general course, count the escorts, mark their general positions, and then break through the escort screen with no moon or the moon ahead at full speed. You then have the convoy's speed from observation and can hit 3-4 pre-picked ships in one run. If they do not detect you (mind you you can see them but not vice versa), you can run with the convoy and reload the tubes.
Otherwise (detected) you make a crash dive and try to survive the following depth charges - as long as you are under the convoy no ASDIC or sound gear will detect or hear you, but once the convoy is ahead .. After diving (being detected or not) you will be out of the game for a while, and have to outrun the convoy again when situation allows.
Good luck
