@Krieghund:

Thanks for your feedback, guys.  This is what we’re currently considering:
Q.  Submarines can attack transports that move through their sea zone “unaccompanied by surface warships”.  Under exactly what conditions may subs attack moving transports?
A.  If at any time during a transport’s movement it finds itself in a sea zone with a submarine belonging to a power with which it is at war and there is no friendly surface warship in the sea zone belonging to a power that is at war with the enemy power, it may be fired upon.

Portions of this were copied from the FAQ response to escorted transports, but I haven’t seen a ruling on it.
Perhaps I’m not clear on movement phases for different units.  Prior to the escort rules for transports nothing actually affected gameplay in the middle of a move.  You could move some, move others, still move more, and it didn’t matter how or in what order as long as it was legal at the end of the move and start of the next phase.  However, with the new rules for unescorted transports, the timing of movement is a rather big deal and can dilute the strategic value of the subs (and the escort rule).  Basically, there are three scenarios that I see:

A)  Units always begin moving at the same time whether moving one space, two, four, etc.  So nothing can “wait” for another unit to catch up and every piece moves individually, even if it’s only moving one space and something else is moving two spaces to arrive at the same territory/seazone.  If this is the case, transports 1 or 2 spaces ahead of warships moving to a enemy subs’ seazone will be fired on if they move into that seazone as the warships haven’t arrived yet.  This seems to me to be the strictest interpretation of simultaneous movement.  It also means you can’t leapfrog a transport through an enemy sub seazone, by which I mean moving a warship its two spaces into a seazone that has an enemy sub, and then moving the transport from a completely different seazone through to the sub/warship seazone and beyond.  Instead, the transport and warship would both move their first space, the sub would take its free shot, the transport (if still alive) would then move and the warship would arrive in the subs seazone.  This follows precedent for the carrier/plane movement, but gives the sub the most opportunities for a hit.

B)  “Faster” units and those moving a greater distance move first.  For example, a fighter, a destroyer and a transport are all moving to this seazone.  The fighter is moving 3 spaces, the destroyer 2 spaces, and the transport 1 space.  The fighter make its first move, the detroyer and fighter then move together, arriving at the transport’s seazone where all three move together to the final seazone, where the lurking sub is.  In this manner you CAN wait, providing you’re moving a shorter distance.  It still complies with everything moving at the same time and you still can’t leapfrog a transport.  It also complies with carrier/plane movement, and gives the sub an advantage only against leapfrogging as ships within a space of the subs seazone, but not in the transports seazone can provide the escort (according to the new errata) with their first move, meeting the transport.

C)  There is no Spoon:  Movement isn’t actually instantaneous and you can all speedy-like move a warship in to cover the transport that will pass through.  In this case, you can choose to leapfrog units and in which order you move your units, moving a warship its two spaces into a seazone that has an enemy sub, and then moving the transport safely through.  This currently complies with how the errata is worded on escorts because I don’t recall any rules as movement as occurring on a space by space basis.  Previous rules specifically address movement as occurring at the same time only in the sense that it’s in the same phase (you can’t move, conduct combat, move with the same unit other than planes) but the escort rule actually comes into effect in the middle of the move, in the cases where you pass through the subs seazone.  This style of movement is the least in keeping with the already established carrier rules, however, as planes are supposed to move individually and at the same time as the carriers.  Maybe this is a simpler rule, but more of an exploit of the phase and I’d rather the sub be able to strategically threaten routes rather than seeing combat moves within combat move.

So which is it?  For what it’s worth (not much) I prefer B with the new errata ruling, although I still think the previous rule of a warship needing to shadow the entire movement, or already being on station in the subs seazone and not moving out of it was equally in keeping with the idea of a escort convoy.  Seazones are big, the warship should really be with it the whole time.