Q: Were there any anti-aircraft regiments -- or any other units, for that matter -- in the same stack with the railroad gun?

Were there any enemy fighter squadrons patrolling in the area? What did the in-game newspaper say about the loss of your bomber?

The RRG has an anti-aircraft value of 0.5; the atomic bomber has 30 hit points. It seems highly unlikely that the RRG by itself could have shot down your bomber.

The description given said "107th Railroadgun Regiment (Philippines) "Divdesmittrešais" - which implies the RRG was alone or had only 1 or two other units in the stack (at 4 they become Divisions as I recall).

The RRG would not have shot it down, even if defended by a max level AAG or SPAA. But if the target area had fighters patrolling over the target they would have.

I personally would recommend going for Nuclear Rockets instead as they cannot be shot down.

3 AA of sufficient level (L4 I think, but maybe even just L3) would be able to shoot down the NUC bomber. Sorry bro.

This is why I prefer Nuclear Rockets if I was to use nukes (I never have, my play style does not account for it) as rockets cannot be shot down.

If you are going to use bombers you have to be super careful. Large stacks with multiple types of land units, fleets with cruisers (cruisers are the naval version of AA), and of course fighters, AA, and SPAA are to be avoided.

However, the blast radius is quite large, so if your bomber can attack a lone unit near a larger stack, or attack a province that has units close to the center, but not on the center dot then you will have better success.

If you want a better bargain for your gold, try buying Level 4 Rockets. Individually they are not as strong as a nuke, but they are much, much cheaper and easier to R&D and build.

11 Level 4 Rockets is about the same as a Level 1 NUC Bomber, and cannot be shot down, has a longer range, and no friendly fire.
Type....................Cost........................................... Range Soft Hard City Air Naval Notes
L1 Nuke Bomber $30k, 10k RA, 500 ME, 250 MP 500km 600 402 198 300 300.... Friendly Fire, Can be shot down
L4 Rocket $2,500, 500 RA, 1k ME, 25 MP............. 800km 38 38 70 0 30............... Cannot be shot down

So, vs ground units you will need 11 - 16 Level Rockets for the same effect, but 5 rockets has greater City damage than a level 1 Nuke, and 11 - 16 rockets will absolutely demolish a max level production center. Whatever is left will be badly damaged with very low morale (and will thus produce less resources). The 800km range and no friendly fire means you can fire directly into battles +62% farther away with no risk to your own troops.

The R&D costs in time and resources are about the same (nukes take slightly more time I think, but rockets cost slightly more rares); but building a L2 Airbase is much easier than building a nuclear reactor.

Be aware that Level 1 rockets are terrible bad. Infantry can shoot those down, so if you are gonna spam don't plan on using the rockets you build until you upgrade to level 2.

PS: If you are gonna be a gold user rocket spammer in your next game please check to see if KingKongo is in the game. If I am please message and ally with me and I will <ahem> help you get the most value for your gold spent by directing you to high value targets that, of course, do not belong to me. xD

@Zimbrisor: I generally agree: for the huge investment in research time and resources, nuclear bombers get shot down too often for my tastes, and nuclear missiles are the better choice under most circumstances.

That said, there are certain circumstances when the bomber provides greater flexibility, including the ability to fly from your air bases to allied air bases to the enemy target. If you and your allies have a well developed air base network, that could be a significant advantage.

Good point, the bombers are definitely far more mobile than the rockets.

Course, if you are counting on allied support, you could avoid the bomber getting shot down by having an ally put a low AA value unit near the desired target, DoW your ally and target the specific unit for the nuclear attack and then re-ally with your partner after the fact..

Never tried it, but the theory seems sound.