Convoy advice please

[kylania]

So I ran into my first convoy tonite, a large one too! After a days of chasing one, and a week of sitting in a spot waiting for others, I came across one directly in my path as I headed home.

The large convoy consisted of 20 ships! 16 merchants and 4 escorts. A Hunt I Destroyer running point, two Flower Corvettes on the port and starboard flanks and a Fiji Light Cruiser inside formation. As far as I could tell the Fiji never got involved in defense, but remained in formation throughout. Two juicy Large tankers formed the core, with a Medium Cargo ahead and a Light Tanker behind.

The conditions were possibly perfect. Low moonlight, calm seas, intercept at 2100. Since the convoy was coming at me I was ahead of it. I read a few threads and decided on a head on surface attack with a surface withdrawal. I got into position aligned about 1km off the Destroyers path between the two port side ranks of the convoy. One Flower Corvette was to my starboard. When the Destroyer got within 2000m I fired a spread of 4 torpedos at a 10 deg spread at the large tankers at a bit of an angle, hoping missed shots would hit anything else. One massively prematurely went off about 500m from me, next to the destroyer, maybe even hit it? Of the others I believe one hit from my crew reaction, but I saw no evident damage. After letting the volley loose I turned hard to starboard and shot past the Flower which was turning towards my last position. It was obvious neither of those escort ships had seen me!

I did a bit of a box move, but got greedy in coming back around. Coming in from their port side, I was seen by the flower corvette which had taken up station again. So I was coming in at about 250 deg to the convoy, 1.5km behind the Flower as it started to turn around. The Hunt I also turned around and beelined right for me. I let loose my two reloaded torps into the training large tanker, and turned and started to run. Aft tube V left a torpedo for the Flower, but I missed.

At first I thought I'd get away again, since I had a big lead on the two escrots, then I noticed the starboard side Flower had also joined and was shooting at me. ALAARRRM!!!! Crash dive, hard to starboard and silent. They spent about an hour depth charging me, but never near me, I was at 120m and never felt a thing, all distant surface drops maybe? After the silence and lost hydrophone contacts I raised to periscope depth and took stock.

Both tankers WERE hit! They were dropping behind now, 6kts compared to the 9kts of the convoy. I surfaced and started to head in, hoping to catch up to them. About 8km behind I noticed a Flower had remained with the two injured ships. Darn! Drop to periscope again and waited a hour or so. Took a look around and they'd finally moved on.

After a while the main group was 20km ahead, one tanker was 14km ahead and the trailing tanker was all alone 8km from me. I flanked in and tried to take out the tankers with my remaining two torps. Both missed or something, both were 359 gyro angle shots on straight line moving slow ships. Argh! Ranges were 3000m and 8000m. One last torpedo was reloaded, I closed to 800m and it hit, but no sinking!

So instead I decided to deck gun it. 20-30 shots later it's nearly underwater but still hasn't sunk. Now the warships are returning, so I dive to 120m again and easily evade. Stay down for 6 hours, check on my ship.. still there. Down for another 8 hours.. still there. Finally 20 hours later I surface and start in with the deck gun again, this time it sinks!!

So 20 ships and I get 1, and only after 20 hours of waiting. What did I do wrong?
What ranges and angles should you try to take out a convoy from? Should I have come in from behind at first?

Thanks for any advice or stories anyone can give. :p