Sub detection in naval cruise

[Taifun]

In a recent move in a game a sub of mine moving by naval cruise did cross a line of hidden enemy ships and was not intercepted in a Surprise Encounter. The following destroyer moving behind in regular movement was Surprised and severely damaged by the hidden enemy ships.
Why was the sub moving by naval cruise not detected or attacked?

[Sugar]

Afaik it`s related to units` xp.

[Etzel]

What type were the hidden ships you are talking about?

[Hubert Cater]

Was the line of ships completely hidden under FoW, or visible, i.e. known to you and subsequently the sub etc.?

[Taifun]

The line of ships was completely hidden under FoW guarding the strait of Sicily. They were a sub and a battleship side by side. My sub passed through them unscathed and I supposed that the strait was free of ships. Then my destroyer moving in regular move bumped into them and suffered 5 damaged.

[Hubert Cater]

Thanks for the info and from what I can gather this is likely correct as a sub does not surprise another sub, regardless of modes for the stationary sub. So if your sub passed directly over a hidden sub then this would make sense why it was not stopped and surprised.

[Taifun]

That makes sense, because the sub seems that it passed directly over the hidden sub. But the adjacent battleship did not detect it or make it stop.

[The Land]

ORIGINAL: Hubert Cater

Thanks for the info and from what I can gather this is likely correct as a sub does not surprise another sub, regardless of modes for the stationary sub.

Switching subjects slightly - while I can imagine the intention behind this, it does result in some pretty ahistoric uses of the Royal Navy's submarines, to cruise around looking to locate U-Boats so waiting destroyers can pounce on them when localised.

I'm pretty sure it's the optimal method of U-boat hunting, and it's a bit of an odd one!

[Hubert Cater]

That's a tricky one for sure, however if the hidden sub is in Silent mode then passing over it with any ship (other than a Destroyer) will leave it undetected. What you describe only occurs when the sub is on the surface in Hunt mode.

[Taifun]

Switching subjects slightly - while I can imagine the intention behind this, it does result in some pretty ahistoric uses of the Royal Navy's submarines, to cruise around looking to locate U-Boats so waiting destroyers can pounce on them when localised.

I'm pretty sure it's the optimal method of U-boat hunting, and it's a bit of an odd one!

You got it wrong that was not the original idea. The idea was to see if the Sicilian passage was free of enemy ship as I relocated the sub near Malta from Gibraltar. But from what I understand in this game a sub moving in naval cruise will not be stopped by another sub, so the hidden enemy sub (by FOW) will not reveal its position.