Okie-dokie, after fiddling around with old saved games trying to get a good setup for testing bombardment and the double adjacency rule I decided the best solution would be to write my own scenario in which I can control all significant elements.
The test setting is Early July '63.
In Galveston at entrenchment level 5 is a CSA stack of **Taylor, a brigade consisting of 4 Inf regiments and a 6 lb pounder, one Columbiad and one 10 lb pounder Parrott.
In Vicksburg is a CSA stack of **Pemberton and the same type brigade and artillery batteries.
The USA has a fleet of 8 Ironclads and two river transports north of Vicksburg and a second fleet with the same units east of Galveston.
I ran the tests in both patch level 1.15 and 1.16b5. Some of the thing I noticed.
1. The rule book and Wiki say that bombardment only happens through the DAR or if a fleet, with the bombardment button pressed, is supporting friendly land units in in an adjacent land region with enemy land units in the same land region. In testing I've discovered that this is not true. If the shore batteries have their bombardment button pressed, or are in a pre-war fort, and a fleet with pressed bombardment button moves into, is standing stationary in, or is leaving an adjacent river or coastal region, bombardment will take place (I will call this the 'Double Bombardment Rule' or DBR for short),
even if there are no land units friendly to the fleet in the shore batteries region. This is totally different than when I learned the game. I'm not saying that it is bad or good, just different.
2. As stated previously, in patch level 1.16b5 no damage is ever done by the DAR nor the DBR. Hits to fleets and shore batteries is always 0, the shore batteries have no cohesion loss, and cohesion loss in the fleet is so low that I can only assume that it is caused by the fleet moving and firing.
3. In 1.15 if the shore batteries are in good shape, if the bombardment is caused by the DAR there are almost always 50 hits inflicted by the shore batteries per adjacent region after the initially entered region (with Galveston there can be 3 when sailing around it's perimeter). Return fire hits were generally around 0 - 2 but seldom more.
4. If bombardment was caused by the DBR, the damage inflicted by the shore batteries was significantly lower (around 20 - 40 hits) with return hits varying between 0 and 4. If this occurred a second or more times, the hits inflicted by the fleet dropped significantly to 0 - 2 hits. This my be due to the fleets lower cohesion during further bombardments or another mechanism unknown to me.
5. There are a number of coastal regions that are not adjacent for the DBR but are for the DAR, notably:
- Northern Mississippi Delta (first region entered when leaving the Mississippi). Movement between here and the Mississippi Mouth will trigger the DAR, but only naval units in the Mississippi Mouth can trigger the DBR.
- Yazoo Confluent (river region north of the river region west of Vicksburg. Same as above, it triggers the DAR but doesn't trigger the DBR.
- Ocracoke Inlet (north-east of Fort Macon, NC). This is actually just a little bit hidden because the tool-tip highlighting of the region shows that the highlighting almost touches Fort Macon, but the dark dividing line is further north. Same as above.
- There may be more such regions, but those are the ones I found while testing.
6. Often during play (patch level 1.15) I've found that shore batteries loss the pressing of the bombardment button. I find myself constantly having to check the button on all the shore batteries that my come into use in that turn. In patch level 1.16b5 during testing I had to repeat a turn a number of times because the DAR did not trigger when it should have and upon inspecting the shore battery I noted that the bombardment button had become un-presse. This happened in the attached game same '116b5 BT3 1'.
I've attached the scenario that I created for testing (BombTest3.scn), plus two saved games from testing; one at patch level 1.115 (115 BT3 1) and the above mentioned one at patch level 1.16b5 (116b5 BT3 1).
BTW learning to build a scenario, even such a simple one, was very ... interesting
Edit: Oh, BTW2: I did run into situations whee the DAR did not trigger with shore batteries not in pre-war forts, but I can't be certain that it didn't occur due to the bombardment button becoming un-pressed, as noted above, but I did not notice it ever happening with pre-war forts.
Edit2: with regards to 5. above, this is of course WAD because to initiate bombardment from a fleet it must be in one of the Exit Point regions of the adjacent land location's harbor.
Relearning what I've forgotten 