Corpen 18
v. 1.2

v. 1.2 changes: horizontal and vertical protection ratings, fire control system rules, armor penetration at range effects, changed Fragile and Rugged effects, Evasion rules, changed ratings of 203mm, 340mm and heavier guns.
v. 1.1 changes: new torpedo attack rules, modified FAC damage rules, adjusted night spotting ranges, clarified hit effects.

Turn Sequence

Corpen 18 Fleet Database

Corpen 18: Steel Dreams.
Statistics for several never-built warship designs of the WWII era.

Corpen 18 is set of rules for representing WWII-era surface ship engagements. It was designed with the intent of producing a fast-playing set of rules under which even large-scale engagements can be played out in a reasonable amount of time, and where combat takes little more time to resolve than movement. This, in my view, makes for a fluid and balanced game. Unlike many other naval games, which focus almost exclusively on the technical characteristics of the ships themselves, Corpen 18 places great emphasis on the importance of the level of training of sailors and officers crewing the ships. At present, the rules include only their "core,", namely WWII surface combat using gunfire and torpedoes. Corpen 18 variants will include air and submarine/ASW operations, more "chrome" rules, and WWI, pre-dreadnought, and late 19th century (Corpen: 1889) periods. The rules include not only ratings for several classes of ships, but also the methodology that was used to derive those ratings, in order to enable the players to rate ship classes that have not been included. While I welcome suggestions and comments on any aspect of the rules, I am particularly interested in comments on ship ratings and rating methodology. Finally, Corpen 18, in naval terminology, is a 180 degree turn executed by a formation of ships without changing their arrangement within the formation.

The game may be played on a hex map or on a tabletop, with each unit of measurement (or a hex, if using a hex grid) representing 4,000m. Each turn represents about 30 minutes of actual time. Each ship model/counter represents 1 vessel (from cruiser upwards), 2 destroyers and other light vessels, or 4 fast attack craft (PT-boats, S-boats, MTBs, MAS, etc.) 

Class: Bismarck BB      Category:  Capital Ship
Movement: 3/3
Fire Control: IV
Main Battery: 8VL        Range: 10    To-hit:  -1/+1/-1
Secondary: 2     Range: 7    To-hit:  --/0/--
Tertiary: U5    Range: 4   To-hit: --/+1/--
Torpedoes: --
Protection: 7R

Category: determines the ship's characteristics during spotting, braving high seas, or vulnerability to certain types of gunfire.
Movement: number of movement points the ship may spend in the first movement phase (first number) and the second movement phase (second number).
Fire Control: Quality of the ship's fire direction systems, influencing its ability to engage targets at long ranges.
Main Battery gunnery: the ship's main battery. Numerical value represents the power of the main battery, VL, L, or H symbols after it indicate very low, low, or high rate of fire.
Range: in hexes or 4km units of measurement.
To-hit: modifier used when resolving gunnery combat, reflecting the number of guns the ship can bring to bear. Numbers represent, in order, modifiers used when unit fires into its forward facing (60 degrees), broadside facing (starboard and port 120 degree sectors,) or aft (60 degrees). -- indicates the battery may not fire into that arc.
Secondary, Tertiary: lighter-caliber guns.
Torpedoes: number of torpedo spreads (4 torpedoes). -- indicates no torpedoes. If torpedo value has two numbers separated by a /, the first number indicates number of torpedo spreads that may be fired in a single combat phase, the second one total number of ready-to-fire torpedo spreads. A parenthesized torpedo number represents reload torpedo spreads. H that follows torpedo value indicates heavy torpedoes (Japanese Long Lances), L indicates light torpedoes (anything less than 533mm in caliber).
Protection: Self-explanatory. R or F that follow the value indicate Rugged or Fragile ship. If a ship has two protection ratings separated by a /, the first rating is used when firing at the Short and Medium range, the second rating is used when the firer is at Long or Extreme range.

First Movement Phase
First Combat Phase
Second Movement Phase
Second Combat Phase

The first value in the ship's movement allowance represents movement points that can be spent in the first movement phase, while the second value movement points for the second movement phase. Each movement point is equivalent to one unit of measurement/hex. Movement points may not be accumulated from one movement phase to the next, or from one turn to the next.

All detected ships are moved first, followed by undetected ships. Within these two categories, ships are moved in the order of their maximum movement allowance, with the slowest vessels moving first, and the fastest last. For the purpose of speed determination, use the highest speed the ship is capable of at the beginning of turn (i.e., if the ship's maximum speed has been reduced due to damage, use the reduced speed). Ships may make an unlimited number of 60 degree turns during their movement, however, they may not change facing in the final hex of their movement unless they use 1 movement point per facing change.

Movement may be affected by the sea state.

Sea State FAC Escort Cruiser Capital Ship
1-3 -- -- -- --
4 -1/-1 -- -- --
5 1/2 -1/0 -- --
6 1/4 -1/-1 -1/0 --
7+ F 1/2 -1/-1 -1/0

-- indicates no effect. 1/2 and 1/4 indicate movement halved and quartered, respectively. F means units may not operate in such weather. Modifiers separated by a / indicate number of movement points subtracted from first and second movement phases, respectively.

DETECTION: conducted at the end of each movement sub-phase. To determine spotting attempts, cross-reference the category of spotting vessel (in the left column) with the category of vessel being spotted (in the top row) to find the range at which the ships are spotted. If the range between ships is equal to or less than the figure in the table, the ship is considered spotted.


Spotter/Spotted Capital Ship Cruiser Escort FAC
Capital Ship 12 8 7 6
Cruiser 8 7 6 5
Escort 7 6 5 4
FAC 6 5 4 2

Units are spotted automatically if the distance is equal or less to the value in the chart.

Night or poor visibility:
Spotting at night or in conditions of limited visibility (fog, squall, etc.) is a more chancy proposition. At the end of each movement phase, each player may attempt to spot each enemy formation (defined as ships in one hex or in a cluster of adjacent hexes, or within no more than 4000m from at least one other unit of the same formation). Only one spotting attempt may be made. Any friendly unit may be designated to make the spotting unit, and the same unit may attempt to spot more than one enemy formation. A successful spotting attempt means all ships within the formation are spotted.

To make a spotting attempt, pick a specific unit within the formation, check the distance, roll 1D10, and consult the table below.

Distance 0-1 2 3 4 5
Spotting Chance 7 5 3 1 -1

Target is Capital Ship: +2
Target is Cruiser: +1
Target is FAC: -2
Formation greater than 4 units: +1
Formation spent at least 2 movement points during the movement phase: +1
Target against shoreline: -4

Spotter Crew Quality is Elite: +2
Spotter Crew Quality is Veteran: +1
Spotter Crew Quality is Experienced: 0
Spotter Crew Quality is Trained: -1
Spotter Crew Quality is Green: -2

Target Crew Quality is Trained: +1
Target Crew Quality is Green: +2

Full Moon: +2
HaU6 Moon: 0
New Moon: -2
Daytime Rain or Haze: 0
Nighttime rain or haze: -2

Effects of Radar: Units with Basic Radar add 2 to spotting chance. Units with Advanced Radar add 4 to spotting chance and double spotting distances.

Radar availability:
Basic: United States, Great Britain, Germany 1940, Japan 1943, Italy 1943, USSR 1944.
Advanced: United States, Great Britain, Germany 1944
Allied navies (Free French, Dutch, Polish) acquire radar at the same time as US and UK.

Stacking: if using a hex grid, at the end of each movement phase no more than two naval units (individual capital ships and cruisers, pairs of escorts, FAC quads) may occupy the same hex.

COMBAT: In this phase opposing ships may attack one another with gunfire and torpedoes. Gunfire and torpedo attacks are resolved simultaneously, with the highest-quality units firing first (with damage being resolved immediately), and lowest-quality firing last. Each of the ship's batteries may only fire once per turn. In other words, if a ship's battery engaged an enemy in the first combat phase, it may not fire again in the second combat phase. Torpedo attacks may be made during either, or both, combat phases, as long as the vessel has torpedoes.

Gunnery Combat:
Determine whether the attacking ship is firing through its Bow, Broadside, or Stern facing. Bow and Stern facings are 60 degree arcs, whereas Broadside arcs are 120 degrees each.
To select initial column, first determine whether the target ship has a split armor rating or not. If the target has two armor ratings, the first armor rating (representing belt armor) is used at Short and Medium ranges (see chart), and the second armor rating is used at Long and Extreme ranges.

Range/Range Band Short Medium Long Extreme
4 1 2 3 4
5 1 2 3 4-5
6 1-2 3 4 5-6
7 1-2 3-4 5 6-7
8 1-2 3-4 5-6 7-8
9 1-2 3-4 5-7 8-9
10+ 1-2 3-5 6-8 9+

Then subtract protection rating of target from gunnery rating of attacker. Note that some batteries have dual ratings, with one rating for use against unarmored vessels (U1-U7), and the other for use against armored vessels. Unarmored vessels are all considered as having protection of 0 if fired upon by batteries with ratings of 1 and higher. Light batteries (with gunnery rating of U1a-U7) may not attack armored targets, with the exception of U7 batteries which are considered to also have a rating of 1. Ships with armor value of 1 may be attacked by ships with U6 batteries on the -2-3 column.

When a vessel with protection of U1-U7 is fired upon by a vessel with a U1-U7 gunnery rating, use the following rules:
If gunnery rating is lower than, equal to, greater by up to 3 than protection rating, determine the difference between ratings and select appropriate column.
If gunnery rating is greater than protection rating by 4 or more, use "+2 +3" column, regardless of the difference between ratings.

Die Roll/Armor difference -7 or less -4... -6 -2-3 -1 0 +1 +2, +3 +4..+6 +7 or more
10 1 1 1 2 2 4 4 4 4
9   1 1 1 2 2 4 4 4
8     1 1 1 2 2 4 4
7       1 1 1 2 2 4
6         1 1 1 2 2
5           1 1 1 2
4             1 1 1
3               1 1
2                 1

Column Shifts: (not applicable to ships with U# protection ratings or fire by U# batteries).
Medium and Long range: 1L

Gunnery modifiers:
Apply to-hit modifiers for the ship's appropriate firing arc (forward/broadside/aft, in that order)

Range modifier: find the appropriate modifier (in the top row) depending on the FireCon rating of the ship and the range at which it is firing.

FireCon/Modifier 0 -2 -4 -6
I 1 -- 2 3+
II 1 2 3-4 5+
III 1 2-3 4-6 7+
IV 1-2 3-4 5-8 9+
V 1-2 3-5 6-10 11+

Ship record indicates FireCon for the Main Battery. Secondary and Tertiary batteries have their FireCons reduced by 1 and 2 levels, respectively.

Evasion modifier:

Target type/Range 0-1 2 3-4 5+
Fast Cruiser (move 6 or higher), slow Escort (move less than 6) 0 0 0 -1
Fast Escort (move 6 or more) or slow FAC (more less than 6) 0 0 -1 -2
Fast FAC (move 6 or higher) 0 -1 -2 -4

Evasion modifiers are doubled for batteries with L rate of fire, and quadrupled for batteries with VL rate of fire. They are ignored by batteries with H rate of fire.

Shooter Crew Quality:
Elite +2
Veteran +1
Experienced 0
Trained -1
Green -2

Target Crew Quality
Elite -2
Veteran -1
Experienced 0
Trained +1
Green +2

Target is Fragile: add number of hits already suffered by the ship.
Target is Rugged: subtract number of hits already suffered by the ship.

Sea State:

Sea State FAC Escort Cruiser Capital Ship
1-3 -- -- -- --
4 -2 -- -- --
5 -4 -2 -- --
6 -6 -4 -1 --
7+ F -6 -2 -1

Each ship's battery may attack only one target per turn (exception: secondary and tertiary batteries, may attack one target per side). However, if the ship's gunnery attack results in the sinking of the target vessel, it may attack another vessel with a -2 modifier. It may continue to do so, with cumulative -2 modifiers.

In case of night combat, warships with crews not rated as Night Fighting-Proficient (NFP) have their Crew Quality reduced by 1 level.

Hit Effects:
Numbers on the CRT represent number of hits suffered by the target. Hits are cumulative from turn to turn, and may not be repaired.

Hits on Capital ships, Cruisers, and Escorts have the following effects: 1 hit represents minor damage, and results in -1 DRM to all subsequent fires. 2 hits: significant damage, -2 DRM, speed reduced by 2 movement points or halved, whichever is smaller. 3 hits: target is reduced to only 1 movement point, -4 on all to-hit rolls. 4 hits: the ship is sunk.

Hits on FACs: 1 hit: significant damage, -2 DRM, speed reduced by 2 movement points or halved, whichever is smaller. 2 hits: FAC is destroyed.

Torpedo Combat:

Designate a target hex (if using a hex grid) or a target vessel (if using other playing surface). Determine number of torpedo spreads launched at the target. Roll for each spread to determine hits.

Hit number depends on range:
0 hexes: 6; 1 hex: 4; 2 hexes: 3; 3 hexes: 2; 4 hexes: 1; 5 hexes: not allowed.

To get the hit number for Light torpedoes, halve the range. To get the hit number for Heavy torpedoes, double the range.

Hit number modifiers: shooter and target crew quality (as for gunnery)
Target is FAC: -4
Attacker is unspotted, or target is otherwise surprised: +2
Sea state: gunfire modifiers are halved.
Evasion: as for gunnery.

A single torpedo spread may be launched against 2 adjacent hexes (or at ships within 4000m within one another), in which case each attack suffers an additional -2 hit number modifier.

After obtaining the final hit number, roll 1D10. If the roll is equal to or less than the hit number, spread score is 1. If the roll is equal to or less than 1/3 of the hit number (round fractions down), the spread score is 2.

Total the number of spread scores for the target, then roll to determine damage for every vessel in the target hex or within 2,000m of the target vessel (if using a normal playing surface) on the "+7 or higher" column, using the following modifiers:

Total score 1: -1; 2: 0; 3: +1; 4: +2; 5: +3; 6 or greater: +4

Additional modifiers:
Target is a merchant vessel: +1. Target is a capital ship (applicable only to modern battleships): -1.

Torpedo hit effects are the same as for Gunnery combat.

Corpen 18 Fleet Database

Corpen 18: Steel Dreams. Statistics for several never-built warship designs of the WWII era.

Mike J.
The J-8 Shop
Wargame Rules and Variants