Convoy raiding

The 36 start and sub build-up makes sense, but that raises another problem. Too many things to try and not enough time to try them :-( :-( :-(

@Warwick:

An escorting vessel is committing its movement for a 6-month period to hunting subs. The DD unit marked as escort off Canada is actually ranging all along the convoy route from Canada to England but in a diffused manner. For game purposes the DD can be attacked in the Canadian coast space, however it is not present to block movement… If combat is conducted in the space the DD is included.

Yes, very well said! Your analogy provides a great explanation from the escort’s perspective. If I turned it around and expanded upon it from the raider’s perspective, it would go something like this.

A raiding sub is committing its movement to hunting convoys, during which it is actually ranging along the convoy route in a diffused manner. For game purposes, the sub is moved to a specific sea zone. While alone there, its placement is a virtual representation of its physical location as it ranges along the convoy line. However, when the SZ contains an escort then its virtual location becomes a physical one. This situation represents the chance encounter of an escort catching a sub “red-handed” i.e. while it is actively attacking a convoy. Therefore, escorts can only fire on a raiding sub if they both occupy the same SZ. All other effects of the DD escort on raiding are represented by and accounted for in the +1 modifier of its defending die roll.

In essence, the escort rules give units  that can’t otherwise detect subs (like a lone DD) the ability to do so. They just went a little overboard by allowing that detection to occur across an entire ocean. I could almost justify a “Raider” marker for subs (a future enhancement, maybe?).

Anyway, we decided to go with the following house rule:

• only an escort in the same sea zone can fire on a raiding sub

• planes from a carrier escort get their full defense roll; all others lack sub detection so get half of their defense roll rounded down but not less than 1

• against advanced subs, no escorts except planes from a carrier escort can fire on the raiding sub; the roll is half their defense rounded down

• the anti-sub warfare rule stands as is

• if advanced subs and anti-sub warfare are both in effect, escorts get +1, convoy lines defend on 2, but transports lose their defense roll

@Warwick:

The escort/raiding rules in GW36 are an imperfect representation of a very complex operation…

I agree 100%. And with just a few tweaks, the rules can better represent the reality of that operation.

Why do you think that raiding is “without risk” to the sub? All other combat rules still apply, so the Allies can send a light carrier and destroyer to take out the sub if they don’t want it raiding.

How does being an escort endanger a DD any more than not being one?

I am concerned about physical positions for good reason. We all want rules that are plausibly based in reality. When rules do that, they make more sense, are easier to remember, and make this historical war simulation we call a ‘game’ more fun.

As you said, the convoy-escort-raider process is a complex operation. Multiple convoys are going/coming along the convoy line all the time. If only one DD is assigned escort duty for 25% of the line (1 sea zone out of 4 between Nova Scotia and England), it is logical to conclude that convoys have no escort over the other 75%. [In fact, not all convoys had escorts until the end of 1942.] So it doesn’t matter if the DD knows where the convoys are going to be – it can’t protect them outside of its own area of patrol (sea zone). FYI by late 1942, the tactic of chasing a sub with ships had become standard practice. See the historical account of Captain John Walker http://www.historynet.com/captain-frederick-john-walker-royal-navys-german-u-boat-menance.htm.

I like HBG’s idea of convoy lines, escorts, and raiders. It just needs some help. Maybe I went too far on the side of raiders – have to try it and see. If you think escorts need a shot against raiders for balance, keep everything as it is but allow an escort only one shot against its nearest raider. Multiple shots makes escorts OP.

We both agree that the whole issue of convoys, escorts, and raiding is very complex and that the existing rules are unbalanced. My proposed changes go farther than just limiting escorts to one roll. Maybe they go too far and create unbalance in the other direction – I don’t know. Only testing will tell.

But after such good discussion, I think I will start with only 2 changes:

1. an escort must be in the same sea zone as a raiding sub to fire on it
2. the escort gets only one defense roll even if multiple subs are raiding in its sea zone

Here’s my last attempt to convince you about #1. In the notes about raiding and escorting (p.77), HBG says twice that the intent of the rules was to force Britain to “spread her ships out along the convoy lines” for escort duty rather than concentrating them into “a large attack force”. Allowing a DD to fire on a sub not in its SZ directly undermines this stated intent.

The Brits aren’t limited to 2 carriers and Germany cannot spend 15 IPP per turn for very long and still expect to win the land war. There are just too many variables to determine a ‘realistic’ sub kill rate for the Brits and I don’t think it’s necessary, anyway. If the Brits dedicate more ships as escorts, the escorts themselves will have the opportunity to sink additional subs beyond the initial 2 per turn.

After doing a more detailed analysis, I have amended my position – raiding is totally broken. I will use two flaws in your analysis to prove it.

@Warwick:

With 2 escort on a line a sub will still produce 1.6 IPC of damage, 1 escort is 2 IPC, while 0 produces 2.9 IPC damage. If one escort gets to fire the numbers move to 2 escort - -0.1 IPC … 1 Escort - 0.5 IPC … 0 Escort 2.9 IPC damage

The first problem is that these calculations are not correct. The average die roll for a d6 is (1 + 7) / 2 = 3.5. Since the same +2 modifier applies to one sub and to 2 escorts, the average raiding rolls will be zero (3.5+2 - 3.5+2 = 0, from my 1st post). For 1 escort the average loss is (3.5 + 2) - (3.5 + 1) = 1/turn/sub; for no escorts it’s 5.5/turn/sub. Since 2 escorts or 1 aircraft on CAP completely nullify a sub’s modifier, if Germany could raid with 1,000 subs then the average raiding loss will still be zero. With escorts returning fire on every raider, 1 CAP fighter will sink 500 of those subs. Ridiculous! Limiting escorts to one shot will still cause German losses of at least 2.5 IPC/turn (fighter 50% chance to hit * 5 IPC/sub). Subs can’t attack fighters, so there’s almost nothing Germany can do about it!

@Warwick:

The UK to cover the 7 atlantic convoy spaces require… the entire DD force the Brits possess plus one
Torpedo Boat… 124 IPC of naval forces tied down in the Atlantic

The intent of the rules (p.77) is to spread the British out, just as you described in your scenario. But doing so is a big mistake and totally unnecessary. One escort protects the entire convoy line. In fact, escorts in only 2 sea zones (21 & 79) will eliminate all raiding losses in the Atlantic and the Med. Just 20 IPC (2 fighters on CAP), not the 124 IPC of navy you suggested, is all the investment needed. And with their navy freed up from escort duty/protection, the Brits can force Germany into an IPC loss for every raid. You showed that the Brits cannot protect 7 convoy spaces and I agree, but now we know they don’t have to. Plus, CAP aircraft can refuse to engage surface ships, so the Axis will have to send planes to sz21 (not gonna happen) and sz79 (more doable but still not easy).

In summary, the current raiding implementation cannot cause Allied losses if escorts are used correctly nor does it force the British to spread its forces out to protect convoy lines. Raiding is broken because:

• 1. the d6 raiding roll is subtracted from the same d6 escort roll
• 2. escort modifiers easily cancel out raider modifiers
• 3. each escort gets a defensive fire roll against all raiders
• 4. limiting defensive fire to one roll/escort only solves problem 3, but that’s not enough to fix raiding

One last comment about this part of your analysis:
@Warwick:

The Axis builds an airbase in Normandy.
The Axis station 2 Medium Bombers and 2 Ftr. Required IPC 21 with 21 existing Air IPC being committed to this operation.
The Axis station Ftr/Float Planes/Medium Bombers on Sardina 2 or so. 11 IPC required.
The Axis builds 3 Subs per turn to support Atlantic operations….

the German Player is spending 15 IPC to attack the Atlantic… Since the German player generally has 45 to 55 points after the Fall of France this is trivial to maintain.

There are several costs in your list that are ignored when you conclude that it will only take “15 IPC to attack the Atlantic” per turn. The costs for units already on the board have to be taken into account. Why? It’s called the opportunity cost. If not allocated to help kill escorts (or whatever), these units would’ve had the ‘opportunity’ to do damage elsewhere. Since some of the costs are one-time and some are per-turn, you have to convert one to the other. Total one-time costs are the airbase = 10 and 6 aircraft = 63. Total per-turn cost is 3 subs = 15. The real cost to attack the Atlantic for 5 turns is (10 + 63 + (15 * 5))/5 = 29.6 IPC/turn; for 10 turns it’s 22.3/turn. That’s roughly half of the German per turn income which I would not call “trivial”.

You are right, my math was off too, can’t use averages with escorts. Here’s a table created from my spreadsheet for raiding sub vs. escorts with +2 modifiers. I shortened it because creating a table was a hassle, no copy/paste :-(

| raider roll - escort roll

| 1 |
| 2 |
| 3 |
| 4 |
| 5 |

| # ways

| 5 |
| 4 |
| 3 |
| 2 |
| 1 |

| expected IPP loss

| 0.14 |
| 0.22 |
| 0.25 |
| 0.22 |
| 0.14 |
| 0.98 |

|

The 2nd col is how many ways the raider minus escort roll can equal the 1st col (i.e. only 1 way to lose 5 from raiding: raider rolls 6, escort rolls 1). There is a 2.8% chance (0.17 * 0.17) for any combination of 2 rolls on a d6. The last column is the 1st col times 2nd col times 2.8%. So when both sides have +2 modifiers, the average IPP loss/turn/sub is 0.98, close enough to 1. If I understood you, it looks like we agree (you originally said 1.6, then said that was too high by 0.6-0.7). By the same method, I calculated 1.56 for 1 escort.  This is for no escorts returning fire.

If escorts get even one return fire, that loses Germany 3.3 IPP/turn for 2 DD escorts. The only way raiding can be profitable for the Axis is against unprotected convoy lines. So keep on raiding and hope your opponent doesn’t read this post.