Shark Attack Submarine

[Lagrange]

The Shark Attack Submarine is designed is designed for the rigors of underwater combat.  Underwater combat is extremely dangerous because there's a 1-in-6 chance of failing a hull integrity check for each hit.  Given this, units should not be to expensive, units should be fast to avoid being hit, units should have long range weapons to be able to hit, and armor beyond ~3 hits his marginal.

The apex predator weapon is an LRT-5, since the next best weapon (a PPC) has less than half the range and larger tube count LRTs risk fewer chances of a hull integrity check.  Thus the key question boils down to: what's a good fast unit with modest armor mounting an LRT-5?  Hence, the Shark.

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Shark Attack Submarine

Mass: 15 tons
Movement Type: Submarine
Power Plant: 135 Fuel Cell
Cruising Speed: 118.8 kph
Maximum Speed: 183.6 kph
Armor: Standard
Armament:
     1 LRT 5
Manufacturer: Unknown
     Primary Factory: Unknown
Communication System: Unknown
Targeting & Tracking System: Unknown
Introduction Year: 3025
Tech Rating/Availability: E/X-D-D-C
Cost: 301,600 C-bills

Type: Shark Attack
Technology Base: Inner Sphere (Standard)
Movement Type: Submarine
Tonnage: 15
Battle Value: 231

Equipment                                          Mass
Internal Structure                                  1.5
Engine                        135 Fuel Cell         5.5
Cruising MP: 11
Flank MP: 17
Heat Sinks:                   1                       0
Control Equipment:                                  1.0
Lift Equipment:                                     1.5
Power Amplifier:                                    0.0
Turret:                                             0.5
Armor Factor                  32                      2

                          Internal   Armor   
                          Structure  Value   
     Front                   2         8     
     R/L Side               2/2       6/6   
     Rear                    2         6     
     Turret                  2         6     


Weapons
and Ammo              Location    Tonnage   
LRT 5                  Turret       2.0     
LRT 5 Ammo (24)         Body        1.0     

Moving at 11/17, it can control the range against just about anything else in the water.   The combination of long range and +4 hit modifier while cruising implies that a 4 gunnery adversary hits just 1-in-36 times while a 4 gunnery Shark hits 10 times as often with 24 shots implying an expected 6 hits (~= 2 kills).  And of course adversaries without the speed or range can be easily dispatched.

A key question here is "turret or not" since that spreads the limited armor.  On the other hand, turrets allow you to keep firing regardless of angle of attack.  Overall, a turret seems slighty better than an extra 8 points of armor, since it allows a unit to choose the angle of attack, effectively increasing the amount of armor.  For example, the Shark can take an LRT-5 attack on the front, rear, and each side (+likely a turret) while maintaining fire if it's lucky with the hull integrity rolls.

Daryk's Sea Wolf (the closest previous custom design I could find) is a good comparator non-turret design with similar (slightly more) armor / cost, at slightly slower speed.  Aside from the turret discussion above, 11/17 seems to have a significant advantage since it allows at least some turn while providing a +4 TMM when cruising (~= having better control and a better target number).

Alternative strategies.

• Big slow many LRT-5 submarine.   Ruled out by hull integrity checks.
• Suicide drone fast submarine.  An extreme example is the Zero sub.  With a velocity advantage of only 4 and only modestly smaller cost, the risk of destruction before being able to close is not worth it.  Of course, on a BV basis this strategy is hard to argue with (37 vs. 231), but I'm worried here about force efficiency on a cost basis.
• Savannah Master Submarine.  You can make a 5 ton submarine move 18/27 with a small laser for 2/9ths the price.  That's a good closing velocity, but the inflexibility of targeting without a turret and the lack of robustness to hits makes this iffy.  Overall, I decided against this since I'd expect morale to be a serious issue due to it's near-suicidal nature.

[Retry]

Worth noting that the savannah master sub model can be made a SRCS drone to turn them unmanned without meaningfully affecting the price.  You can do something similar with a 9-ton drone and LRTs as well, if you give up the turret and some of the speed (which is already far higher than anything else under the sea).

[Lagrange]

Worth noting that the savannah master sub model can be made a SRCS drone to turn them unmanned without meaningfully affecting the price.

I can only make this work at 11/17 with a small laser---seems nonviable since the Shark can generally keep the range and LRT it to death.

You can do something similar with a 9-ton drone and LRTs as well, if you give up the turret and some of the speed (which is already far higher than anything else under the sea).

There are tough tradeoffs here, but I'm skeptical that half price is worth reducing the expected hits to kill from 3ish to 1.5ish and making it a factor of 1.5 or 3 easier to hit (at least with regular gunners).  The disparity in +4 TMM vs +1 AMM is quite nice.

[Daryk]

I used a fusion engine for mine: https://bg.battletech.com/forums/index.php/topic,74692.0.html

[Lagrange]

I used a fusion engine for mine: https://bg.battletech.com/forums/index.php/topic,74692.0.html

Yeah, I thought about this.  Ultimately, I decided against it because the extra endurance didn't make sense in a short duration craft with no quarters and no cargo.  The base 450 km range of a fuel cell engine plausibly matches the air/food available for crew by default.   Stated another way, you can usually get within 200km of an LRT target before launching a Shark. 

I honestly haven't found a good justification for a deep sea many-months-endurance sub in 3025 Battletech.

[Daryk]

Those would be for "fleet in being" kinds of things...

[Retry]

I can only make this work at 11/17 with a small laser---seems nonviable since the Shark can generally keep the range and LRT it to death.

The basic SRCS package does not cost tonnage when the vehicle is under 9 tons, so speed wouldn't be affected at all.

There are tough tradeoffs here, but I'm skeptical that half price is worth reducing the expected hits to kill from 3ish to 1.5ish and making it a factor of 1.5 or 3 easier to hit (at least with regular gunners).  The disparity in +4 TMM vs +1 AMM is quite nice.

Not seeing where you got these numbers from.  A 9-ton FCE boat can be made 10/15 with the same hull armor profile except for 2 points in the rear.  That does not translate to halving the # hits to kill or making it 3x easier to hit.

[Cavgunner]

I have just one question.

Is it a shark attack submarine, or a "Shark" attack submarine?

[Daryk]

I read it as the latter...

[Cavgunner]

My bro, I am joking.

[Lagrange]

Those would be for "fleet in being" kinds of things...

The threat of naval force seems plausibly irrelevant across most worlds since control of commerce to/from the planet is a strong lever for control of the planet.   Every split ownership world is a typically short-term exception.

The basic SRCS package does not cost tonnage when the vehicle is under 9 tons, so speed wouldn't be affected at all.

Ah, good.  MML is off here.  The Savannah Master Sub might look like:

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Savannah Master Submarine

Mass: 5 tons
Movement Type: Submarine
Power Plant: 60 Fusion
Cruising Speed: 194.4 kph
Maximum Speed: 291.6 kph
Armor: Standard
Armament:
     1 Small Laser
Manufacturer: Unknown
     Primary Factory: Unknown
Communication System: Unknown
Targeting & Tracking System: Unknown
Introduction Year: 3025
Tech Rating/Availability: E/X-D-D-C
Cost: 66,875 C-bills?
Battle Value: 71

Equipment                                          Mass
Internal Structure                                  0.5
Engine                        60 Fusion             2.5
Cruising MP: 18
Flank MP: 27
Heat Sinks:                   10                      0
Control Equipment:                                  0.5
Lift Equipment:                                     0.5
Power Amplifier:                                    0.0
Armor Factor                  8                     0.5

                          Internal   Armor   
                          Structure  Value   
     Front                   1         3     
     R/L Side               1/1       2/2   
     Rear                    1         1     


Weapons
and Ammo              Location    Tonnage   
Small Laser            Front        0.5     
The 18 move is good for a +5 TMM which helps, but the lack of a turret, range 1/2/-, and -4 initiative penalty make success in targeting pretty iffy.  That's about a 10% chance of winning initiative, so in a 4-on-1 as suggested by pricing, the Shark could often just arrange to be at range 7 vs. it's preferred target, so the target number if 4+1(cruise)+5(TMM)=10.  If the SM subs win initiative, then the Shark would face 1 to 4 small laser attacks at range 1 with a target number of 10 or 11 = 5+4+(1 or 2).   Overall, I expect the Shark seems likely to break even?  The inflexibility of robot command still seems to plausibly favor the Shark approach.   You could use lower speeds to gain extra tons for a medium laser (short range to 2), a turret, or extra armor so that it survives more hits.  Maybe something there is compelling?  The difficulty with a lower speed is that the TMM will suffer and at an actual Savannah Master engine it will just tie the Shark in speed.

Not seeing where you got these numbers from.  A 9-ton FCE boat can be made 10/15 with the same hull armor profile except for 2 points in the rear. 

You are thinking of this:

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Robotic LRT Submarine

Mass: 9 tons
Movement Type: Submarine
Power Plant: 60 Fuel Cell
Cruising Speed: 108 kph
Maximum Speed: 162 kph
Armor: Standard
Armament:
     1 LRT 5
Manufacturer: Unknown
     Primary Factory: Unknown
Communication System: Unknown
Targeting & Tracking System: Unknown
Introduction Year: 3025
Tech Rating/Availability: E/X-D-D-C
Cost: 164,536 C-bills?
Battle Value: 183

Equipment                                          Mass
Internal Structure                                    1
Engine                        60 Fuel Cell            2
Cruising MP: 10
Flank MP: 15
Heat Sinks:                   1                       0
Control Equipment:                                  0.5
Lift Equipment:                                     1.0
Power Amplifier:                                    0.0
Armor Factor                  24                    1.5

                          Internal   Armor   
                          Structure  Value   
     Front                   1         8     
     R/L Side               1/1       6/6   
     Rear                    1         4     


Weapons
and Ammo              Location    Tonnage   
LRT 5                  Front        2.0     
LRT 5 Ammo (24)         Body        1.0     
So half the price, 10/15, no turret, risky rear armor, and gunnery 5 / piloting 6 (since the improved version costs a ton on small units).

It's possible to pick up a +4 TMM with cruise speed, but significantly more difficult than with 11/17 since you can't turn.  This is exacerbated by the lack of a turret.  Overall, I think you need to use flank speed typically, which creates opportunities for side slip.   Consider Robot vs. Shark.  If you move flank speed and attack, the target number is 13=5+2(flank)+4(TMM)+2(medium range) vs. Shark's 11=4+1(cruise)+4(TMM)+2(medium).   When Robot is lucky and can go straight and fire, it's 12=5+1(cruise)+4(TMM)+2(medium range).  11 vs. 12 is a factor of 3 disparity in attacks on target while 11 vs 13 is a factor of infinity.  If Robot sticks with cruise always, then you'll often see the Shark attacking 10=4+1(cruise)+3(TMM)+2(medium) vs. Robot's 12=5+1(cruise)+4(TMM)+2(medium range), a factor of 6 disparity.   If Robot instead decides to not move, then it looks like Shark's 9=4+1(cruise)+4(long) vs. Robot's 13=5+4(TMM)+4(long).  Overall a +1 and often +2 disparity in targeting matters a great deal with fast units.  Keep in mind that Robot has a -4 penalty to initiative so disadvantageous geometries could easily result in Robot simply being unable to fire.

Then, let's consider defense.  The situation is better than I realized since you have more tonnage in armor.  It's still worse though---after 1 hit on the front doing 3, 4, or 5 damage (5/6th chance), every hit threatens destruction, and Robot can't turn away and attack.  Shark can turn away and attack, eliminating the possibility of destruction via armor destruction on a facing.  In addition, the Turret may suck up the first hit (1/6th chance) allowing for more forward fire.  Overall, Shark has an edge defensively.

I'm still seeing Shark as having an advantage.   Is it a 2:1 advantage which we would want for a half price unit?  Maybe---we'd need to play it out many times to get a good sense of this.

There is one other difficulty with SRCS---it's sort of like clan machine guns.  That is, there is no technical reason why the IS couldn't build them (tech level C), but it's listed as extinct IS tech in 3025.

Is it a shark attack submarine, or a "Shark" attack submarine?

Yes :-)

[Retry]

Ah, good.  MML is off here.  The Savannah Master Sub might look like:

Maybe it's an older copy of MML?  I've got one of the semi-recent ones and it calculates the drone weight correctly.

Overall, I think you need to use flank speed typically, which creates opportunities for side slip.

I'd double check the rules on side-slipping.  I'm very certain that Subs don't side-slip, that's more a hovercraft and VTOL specific thing.

There is one other difficulty with SRCS---it's sort of like clan machine guns.  That is, there is no technical reason why the IS couldn't build them (tech level C), but it's listed as extinct IS tech in 3025.

I don't really have an answer to this.  Unfortunately there's a lot of canonical things in the BT universe that... don't really make sense.

I'm not suggesting the Shark is outperformed by these drones; they're clearly not.  I'm saying both the "sea savannah master" and the robot LRT platform are both viable approaches with distinct advantages, being lighter, cheaper, and unmanned (which saves on both actual cost and opportunity costs in the required training of midget sub personnel, another logistical sink).  Sharks compare well to both drones, but what if your opponent uses more normal naval boats like Neptunes instead?  For interdicting those and any maritime supply ships, the drone packs accomplish the same mission just as well despite their limitations in initiative.

If the opponent does have Sharks though, it's trickier, as you say the Shark does have its own significant advantages due to good speed, range, and initiative.  As a very rough guess, I'd bid a drone company of 2x Sea Savannah lances (either your suggested one or a slower 15/23 one with 3x the armor) and 1x LRT drones vs a lance of Shark drones, at roughly equal C-Bill cost.  Assuming initiative is going to be lost more often than not, the Sea Savannahs should move first, with the first 3 trying to get close to the circle of the Shark formation with a high +4 TMM, accepting they're not going to get a targeting solution this turn, using the rest of the Sea Savannahs to latch onto a Shark's 1-hex spot as they move in the turn order, and then finally move the LRT drones last seeking a to-hit range of 7 after 3 of 4 Wolves have moved.

The Sharks may still win, but it's unlikely they will without taking some serious attrition throughout many engagements, even when winning initiative most of the time.

[Lagrange]

I'd double check the rules on side-slipping.  I'm very certain that Subs don't side-slip, that's more a hovercraft and VTOL specific thing.

You appear correct.  Very nice---it makes using flank speed around underwater obstacles much more reasonable.  A related issue is the turn mode rules in TO which apply regardless of cruise/flank.

I don't really have an answer to this.  Unfortunately there's a lot of canonical things in the BT universe that... don't really make sense.

Yeah, the whacky thing about clan machine guns is that a tech can manufacture them in their workshop.

I'm saying both the "sea savannah master" and the robot LRT platform are both viable approaches

I agree.

If the opponent does have Sharks though, it's trickier, as you say the Shark does have its own significant advantages due to good speed, range, and initiative.  As a very rough guess, I'd bid a drone company of 2x Sea Savannah lances (either your suggested one or a slower 15/23 one with 3x the armor) and 1x LRT drones vs a lance of Shark drones, at roughly equal C-Bill cost.  Assuming initiative is going to be lost more often than not, the Sea Savannahs should move first, with the first 3 trying to get close to the circle of the Shark formation with a high +4 TMM, accepting they're not going to get a targeting solution this turn, using the rest of the Sea Savannahs to latch onto a Shark's 1-hex spot as they move in the turn order, and then finally move the LRT drones last seeking a to-hit range of 7 after 3 of 4 Wolves have moved.

The Sharks may still win, but it's unlikely they will without taking some serious attrition throughout many engagements, even when winning initiative most of the time.

The strategy above doesn't quite work if you are using lance movement (as per TO page 24)---then it's 90% of the time you move everything first.   Another intrinsic issue is that the robots can only function according to programming and there's a limited set of programs available per IO pages 154-158.  Which would you use?  It's more restricted than you suggest above.  For example, movement-wise, the priorities are: Front towards enemy > enemy rear > preferred range > highest TMM > lowest AMM which is further modified by aggressiveness.