Here below, the changes (bolded or strike-through) on the 1942.2 OOB rules which, I believe, will simplify units interactions:
A&A 1942 Second Edition, p. 31:
TRANSPORTS
Cost: 7
Attack: 0
Defense: 0 1*
Move: 2
Hit value: 1
Escort Convoy Defense: * single roll @1 each combat round for any number of friendly Transports present in SZ.
Unit Characteristics
No Combat Value Non warship combat unit: Even though a transport can attack or defend, either alone or with other units, it has very little combat value of 0. This means that a transport cannot fire in the attacking unit’s or the defending unit’s fire steps but can roll in defending unit’s fire step a single die @1 per combat round for all friendly Transports in an embattled Sea-Zone. Transports may not attack without being accompanied by at least one unit with an attack value, unless they are conducting an amphibious assault from a friendly sea zone that is free of enemy submarines. This lack of an effective combat capability also allows enemy ships to ignore the presence of transports.
Doesn’t Block Enemy Movement:
Any sea zone that contains only enemy transports doesn’t stop the movement of a sea unit. Air or sea units (other than transports) ending their combat movement in a sea zone containing only enemy transports automatically destroy can attack those transports (unless they are ignoring them to support an amphibious assault instead). This counts as a sea combat for those sea units. Sea units can also end their noncombat movement in a sea zone containing only enemy transports.
Chosen Last: Owner’s choice of casualty order:
Transports can only be chosen as a casualty anytime, the same way as if there are no other eligible units. Normally but not necessarily this will be possible, but it can also occur in mandatory way under special circumstances. For example, submarines attacking surviving transports and planes, in a given combat round, will hit transports because they can never hit planes. fighters attacking transports and submarines will hit the transports because they cannot hit the submarines without a friendly destroyer present.
OPTIONAL (nearer OOB, both mechanic and balance):
Chosen Last:
Transports can only be chosen as a casualty if there are no other eligible units. Normally this will occur when only transports are left, but it can also occur under other circumstances. For example, submarines attacking surviving transports and planes, in a given combat round, will hit transports because they can never hit planes. fighters attacking transports and submarines will hit the transports because they cannot hit the submarines without a friendly destroyer present.
Carry Land Units:
A transport can carry land units belonging to you or to friendly powers. Its capacity is any one land unit, plus one additional infantry. Thus, a full transport may carry either two infantry or a tank, an artillery, or an antiaircraft artillery unit plus an infantry. A transport cannot carry an industrial complex. Land units on a transport are cargo; they cannot attack or defend while at sea and are destroyed if their transport is destroyed.
Loading and Offloading:
A transport can load cargo from one or two territories in or adjacent to friendly sea zones that it occupies before, during, and after it moves. A transport can pick up cargo, move one sea zone, pick up more cargo, move one more sea zone, and offload the cargo at the end of its movement. It can also remain at sea with the cargo still aboard (but only if the cargo remaining aboard was loaded in a previous turn, was loaded this turn in the Noncombat Move phase, or was loaded this turn for an amphibious assault from which the transport retreated).
Loading onto and/or offloading from a transport counts as a land units entire move; it can’t move before loading or after offloading. Place the land units alongside the transport in the sea zone. If the transport moves in the Noncombat Move phase, any number of units aboard can offload into a single friendly territory.
Land units belonging to friendly powers must load on their controller’s turn, be carried on your turn, and offload on a later turn of their controller. This is true even if the transport remains in the same sea zone.
Whenever a transport offloads, it cannot move again that turn. If a transport retreats, it cannot offload that turn. A transport cannot offload in two territories during a single turn, nor can it offload cargo onto another transport. A transport cannot load or offload while in a hostile sea zone. Remember that hostile sea zones contain enemy units, but that for purposes of determining the status of a sea zone, submarines and transports are ignored.
A transport can load and offload units without moving from the friendly sea zone it is in (this is known as “bridging”). Each such transport is still limited to its cargo capacity. It can offload in only one territory, and once it offloads, it cannot move, load, or offload again that turn.
Amphibious Assaults:
A transport can take part in an amphibious assault step of the Conduct Combat phase. That is the only time a transport can offload into a hostile territory.
During an amphibious assault, a transport must either offload all units that were loaded during the Combat Move phase or retreat during sea combat. It can also offload any number of units owned by the transports power that were already on board at the start of the turn.
A&A 1942 Second Edition, p. 13:
TRANSPORTS
If a transport encounters hostile surface warships (not enemy submarines and/or transports) AFTER it begins to move (not counting the sea zone it started in), its movement for that turn ends, and it must stop there and conduct sea combat.
A transport can load units while in any friendly sea zone along its route, including the sea zone it started in. If a transport loads land units during the Combat Move phase, it must offload those units to attack a hostile territory as part of an amphibious assault during the Conduct Combat phase, or it must retreat during the sea combat step of the amphibious assault sequence while attempting to do so. A transport that is part of an amphibious assault must end its movement in a friendly sea zone (or one that could become friendly as result of sea combat) from which it can conduct the assault. However, a A transport is not allowed to offload land units for an amphibious assault in a sea zone containing one or more ignored enemy submarines unless at least one warship belonging to the attacking power is also present in the sea zone at the end of the Combat Move phase.
Any land units aboard a transport are considered cargo until they offload. Cargo cannot take part in sea combat and is destroyed if the transport is destroyed.
A&A 1942 Second Edition, p. 29:
DESTROYERS
Cost: 8
Attack: 2
Defense: 2
Move: 2
Unit Characteristics
Anti-sub Vessel:
Destroyers are specially equipped for anti-submarine warfare. As a result, they have the capability of cancelling many of the unit characteristics of enemy submarines.
A destroyer cancels the Treat Hostile Sea Zones as Friendly unit characteristic of any single enemy submarine that moves into the sea zone with it. This means that the submarine must immediately end its movement, whether combat or noncombat, upon entering the sea zone. If a submarine ends its combat movement in a sea zone with an enemy destroyer, combat will result.
If a destroyer is in a battle, it cancels the following unit characteristics of all enemy submarines in that battle: Surprise Strike, Submersible., and Cannot Be Hit By Air Units. Note that destroyers belonging to a power friendly to the attacker that happen to be in the same sea zone as the battle do not actually participate in it; therefore, they do not cancel any of these characteristics of defending submarines.
A&A 1942 Second Edition, p. 30:
SUBMARINES
Cost: 6
Attack: 2 Surprise strike
Defense: 1 Surprise strike
Move: 2
Unit Characteristics
Submarines have several unit characteristics. Most of them are either cancelled or stopped by the presence of an enemy destroyer.
Surprise Strike:
Both attacking and defending submarines can make a Surprise Strike by firing before any other units fire in a sea battle. As detailed in step 2 of the General Combat sequence (pg. 16), submarines make their rolls before any other units~~, unless an enemy destroyer is present~~. All Submarine units keep their Surprise Strike in all circumstances. If no submarine from neither side is eligible for a Surprise Strike, there is no step 2. Players move directly to step 3 of the General Combat sequence.
Submersible:
A submarine has the option of submerging. It can do this anytime it would otherwise make a Surprise Strike.
The decision is made before any dice are rolled by either side (the attacker decides first) and takes effect immediately. When a submarine submerges, it is immediately removed from the battle strip and placed back on the map. However, a submarine cannot submerge if an enemy destroyer is present in the battle.
Treat Hostile Sea Zones as Friendly:
A submarine can move through a sea zone that contains enemy units, either in combat or noncombat movement. However, if a submarine enters a sea zone containing an enemy destroyer, it must end its movement there. If it ends its combat move in a hostile sea zone, combat will occur.
Does Not Block Enemy Movement:
The “stealth” ability of submarines also allows enemy ships to ignore their presence.
Any sea zone that contains only enemy submarines does not stop the movement of a sea unit. Sea units ending their combat movement in a sea zone containing only enemy submarines may choose to attack them or not. Sea units can also end their noncombat movement in a sea zone containing only enemy submarines.
Cannot Hit Air Units or Submarine Units:
When attacking or defending, submarines cannot hit air units nor other submarine units.
Cannot Be Hit by Air Units:
When attacking or defending, hits scored by air units cannot be assigned to submarines unless there is a destroyer that is friendly to the air units in the battle.
A&A 1942 Second Edition, p. 26:
AIR UNITS
Air units can hit submarines only if a friendly destroyer is in the battle. Whenever a round of combat starts and there is no enemy destroyer, submarines cannot be hit by air units.