UB-20-Class Submarine
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UB-20-Class Submarine | |
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Service Information | |
| Nation | Republic of Gondara |
| Branch | Republic of Gondara Navy |
| Class | UB-20-class |
| Type | Long-range raiding submarine |
| Role | Surface commerce raiding, deep-ocean patrol, maritime interdiction, scouting |
| Operator | Republic of Gondara Navy
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Construction | |
| Commissioned | 1920 |
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General Characteristics | |
| Surfaced displacement | 1,200 long tons standard |
| Submerged displacement | ~1,700 long tons |
| Length | ~265 ft |
| Beam | ~24 ft |
| Draft | ~14.5 ft |
| Complement | ~46 |
| Patrol endurance | ~50 days
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Hull and Diving | |
| Hull construction | Riveted high-tensile Gondaran steel |
| Hull form | Ocean-going double-hull form optimized for surface running and rapid submergence |
| Operating depth | ~50 m |
| Test depth | ~60 m |
| Crush depth | ~90 m effective
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Propulsion and Performance | |
| Propulsion | Twin-shaft diesel / battery-electric |
| Diesel plant | 4 × ~1,200 bhp marine diesels |
| Electric plant | 2 × ~500 shp electric motors |
| Shafts | 2 |
| Surface speed | 19.5 kn |
| Battery speed | 7 kn maximum |
| Combat range | 7,000 nmi at 12 kn |
| Battery endurance | ~50 nmi at 4 kn |
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Sensors and Fire Control | |
| Passive sonar | Passive hydrophone array |
| Active sonar | None |
| Fire control | Manual plotting with mechanical torpedo-angle aids |
| Periscopes | Attack and observation/navigation periscopes |
| Communications | Surfaced wireless telegraph and radio receiving equipment
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Armament | |
| Torpedo tubes | 8 × 550 mm (6 bow, 2 stern) |
| Weapons carried | 8 torpedoes; tube loads only, no reloads |
| Deck gun | 2 × 106.25 mm submersible wet guns |
| Anti-aircraft | 2 × twin 12.5 mm heavy machine-gun mounts |
The UB-20-class submarine is a long-range raiding submarine operated by the Republic of Gondara Navy. Entering service in 1920, the class was developed specifically for long-distance Pacific operations and represents the first mature expression of Gondara's submarine-raider doctrine.
The UB-20 is fundamentally a surface raider capable of submerging. Strategic movement, reconnaissance, pursuit, and much of its commerce-raiding activity are conducted on the surface, where powerful diesel machinery provides a maximum speed of 19.5 knots and an unusually high long-range cruising performance of approximately 7,000 nautical miles at 12 knots.
Submergence is used principally for concealed torpedo attack, positioning, evasion, and survival.
The class therefore does not attempt to maximize underwater performance. Maximum submerged speed is only 7 knots, and the battery system provides approximately 50 nautical miles at 4 knots under favorable conditions.
Instead, engineering effort is concentrated upon sustained surface mobility and exceptionally rapid transition from surface to submerged operation. From alert posture, a UB-20 can reach periscope depth in approximately 40 seconds.
The armament reflects the same philosophy. Eight 550 mm torpedo tubes provide a powerful immediately available torpedo battery, but the submarine carries no reload torpedoes. Surface attack is instead supported by two 106.25 mm submersible wet guns.
The UB-20 is therefore neither a conventional torpedo submarine nor a small submarine cruiser. It is a purpose-built Pacific raider whose principal weapons are strategic mobility, surprise, surface gunfire, and the ability to disappear rapidly beneath the surface when threatened.
Development and Design
Development of the UB-20 began during the closing years of the First World War as Gondaran naval planners examined the problems created by the enormous distances of the South Pacific.
Even operations around Gondara itself required long transits. A submarine intended to raid distant shipping routes could therefore not be optimized solely around maximum theoretical endurance at very low speed.
The Navy instead required a vessel capable of maintaining a useful strategic cruising speed for prolonged periods.
This produced an early design priority that would remain characteristic of later Gondaran naval vessels:
- Distance traveled per day was treated as a combat capability.
The UB-20 was therefore designed around powerful and efficient marine diesel machinery, substantial fuel capacity, strong surface seaworthiness, and a relatively slender ocean-going hull.
Its maximum surface speed of 19.5 knots is high for a submarine entering service in 1920, but maximum speed was not the principal objective.
The more important requirement was the ability to travel approximately 7,000 nautical miles at 12 knots.
This allowed a UB-20 to shift patrol areas, move ahead of changing shipping routes, respond to reconnaissance information, and escape an increasingly defended operating area without reducing transit speed to the very low economical speeds normally associated with maximum submarine range.
Considerable displacement and internal volume were devoted to propulsion, fuel, and the requirements of prolonged surface operation.
Other capabilities were deliberately limited to preserve this emphasis.
The submarine carries no internal torpedo reloads, its battery-electric installation is modest, and maximum submerged speed is only seven knots.
The design was not intended to achieve superior performance in every operating condition.
It was intended to be exceptional in the conditions that Gondaran planners expected to determine the success or failure of a Pacific raider.
Foreign Technical Exploitation
The UB-20 was an indigenous Gondaran design, but its final development benefited substantially from technical information obtained from former German submarines following the First World War.
Postwar Allied control of surrendered German submarines provided Gondaran engineers with opportunities to inspect German ocean-going designs, review technical documentation, examine machinery and internal arrangements, and compare German wartime experience against Gondara's own developing submarine concepts.
The German U-135 and related boats were particularly important technical benchmarks.
U-135 displaced approximately 1,175 tons surfaced, placing it extremely close to the UB-20 in overall size. The German boat combined powerful diesel propulsion, long ocean-going endurance, multiple torpedo tubes, heavy deck armament, and unusually compact crew requirements.
Its existence provided direct confirmation that a submarine in the approximately 1,200-ton range could combine substantial diesel machinery, heavy surface armament, ocean-going endurance, and rapid submergence.
Gondaran engineers did not reproduce the German design.
Instead, German experience influenced several aspects of the developing UB-20.
Torpedo Battery
Early UB-20 studies had envisioned a smaller four-tube torpedo battery.
Examination of German submarine arrangements demonstrated the tactical value of a larger immediately available torpedo battery, particularly when several weapons could be fired without first maneuvering the submarine through a substantial change of heading.
The final UB-20 therefore adopted:
- 6 × 550 mm bow tubes
- 2 × 550 mm stern tubes
Gondara did not adopt the German practice of carrying a substantial torpedo reload allowance.
Instead, the eight weapons loaded into the tubes constitute the submarine's entire torpedo inventory.
This produced a distinctly Gondaran compromise.
The submarine gained a powerful initial torpedo salvo while eliminating much of the internal storage volume, handling equipment, and additional weapons weight required for reload torpedoes.
That capacity was instead available for fuel, machinery, stores, and other requirements of long-range surface raiding.
Rapid-Diving Practice
German large-submarine experience also contributed to Gondaran understanding of rapid submergence.
Gondaran engineers studied ballast arrangements, venting, free-flooding external structures, diving controls, pressure closures, trim practices, and the sequence of actions required to take a large surface-running submarine underwater quickly.
These lessons reinforced an existing Gondaran requirement that rapid diving be treated as a primary survival characteristic rather than merely a routine operating evolution.
The resulting UB-20 was designed around an approximately 40-second transition from alert posture to periscope depth.
Foreign technical information therefore accelerated and refined UB-20 development without determining its basic design philosophy.
The resulting submarine differed substantially from the German boats that informed it, particularly in surface speed, cruising-speed emphasis, torpedo stowage, weapons distribution, and propulsion priorities.
Hull and Construction
The UB-20 uses an ocean-going double-hull arrangement built principally from riveted high-tensile Gondaran steel.
Approximate dimensions are:
| Characteristic | Specification |
|---|---|
| Standard surfaced displacement | 1,200 long tons |
| Submerged displacement | ~1,700 long tons |
| Length | ~265 ft |
| Beam | ~24 ft |
| Draft | ~14.5 ft |
| Complement | ~46 |
The external hull and casing are designed primarily for good surface behavior while retaining the ability to flood rapidly during an emergency dive.
Free-flooding structures are arranged to minimize trapped air and unnecessary resistance during submergence.
Surface seaworthiness remains important because normal Pacific patrol operations require the boat to spend substantial periods exposed to open-ocean conditions.
Habitability is limited by later standards, but accommodations and stores are sufficient for patrols of approximately 50 days.
Diving Capability
The UB-20 is not designed as a deep-diving submarine.
Its approximate depth envelope is:
- 50 m — Operating Depth: Maximum authorized routine operational depth.
- 60 m — Test Depth: Depth used to demonstrate structural and systems margin beyond normal operations.
- ~75 m — Damage Threshold: Pressure-related leakage, distortion, and system casualties become increasingly likely.
- ~90 m — Effective Crush Depth: Depth at which cascading structural and systems failures make loss of the submarine effectively unavoidable.
The relatively conservative depth capability reflects the class's priorities.
Displacement and engineering effort are concentrated upon surface mobility, rapid submergence, and long-distance operations rather than unusually deep diving.
Crash Diving
The UB-20 can reach periscope depth from alert posture in approximately 40 seconds.
Alert posture assumes that the submarine is already operating in potentially hostile waters with watertight integrity substantially prepared, essential topside personnel kept to the minimum required for safe surface operation, and diving systems immediately available.
The forty-second standard does not apply while the boat is committed to a surface-gunnery engagement, conducting major topside maintenance, or operating under another condition in which exposed personnel and equipment must first be secured.
Rapid diving is treated as a survival system.
The UB-20 spends much of its strategic patrol on the surface and therefore accepts greater exposure to aircraft, surface patrols, and unexpected enemy contact than later underwater-oriented submarines.
Its principal defense against such threats is not prolonged surface combat.
It is the ability to disappear.
Propulsion and Endurance
The UB-20 uses twin-shaft diesel and battery-electric propulsion.
Surface power is provided by approximately:
- 4 × 1,200 bhp Gondaran marine diesels
- ~4,800 bhp combined maximum output
- 2 shafts
The four-engine arrangement reflects Gondara's emphasis on long-distance cruising efficiency and machinery redundancy.
Maximum surface speed is approximately:
19.5 knots
The diesel installation is designed not merely around maximum rated power but around efficient sustained operation at the speeds used during Pacific strategic transit.
The class has an approximate strategic range of:
7,000 nautical miles at 12 knots
This figure represents the defining characteristic of the propulsion plant.
A greater theoretical range could be obtained at substantially lower speed, but Gondaran doctrine places greater value upon useful transit speed than upon achieving the largest possible endurance figure under artificial economy conditions.
Normal fuel capacity is approximately:
180 long tons of diesel oil
The four-engine arrangement also provides considerable machinery redundancy. Damage or failure affecting one engine does not necessarily disable the complete propulsion line.
Submerged Propulsion
Submerged propulsion is deliberately modest.
The submarine carries approximately:
- 2 × 500 shp electric motors
- ~1,000 shp combined
- 2 shafts
Maximum submerged speed is approximately:
7 knots
Maximum underwater speed is intended for tactical maneuver rather than prolonged operation.
At approximately 4 knots, submerged range is about:
50 nautical miles
The battery-electric plant is therefore sufficient for concealed approach, attack, evasion, and local underwater maneuver but is not intended for strategic submerged movement.
This limitation is deliberate.
The UB-20 is a surface raider that can fight and survive underwater, not an underwater warship.
Armament
Torpedo Battery
The UB-20 carries eight 550 mm torpedo tubes:
- 6 × bow tubes
- 2 × stern tubes
The total torpedo allowance is:
8 torpedoes
Every torpedo carried is already loaded in a tube.
The submarine carries no reload weapons.
The six-tube bow battery provides a powerful initial concealed strike against warships, defended merchantmen, transports, or other targets for which surface gunfire would be unsuitable.
The two stern tubes permit attack during withdrawal or defensive fire against a pursuing vessel without requiring the submarine to reverse course.
Once the torpedo battery has been expended, the UB-20 must return to a supporting base or tender to rearm.
The limited torpedo allowance is an intentional consequence of the class's surface-raiding doctrine.
Internal volume that would otherwise be occupied by reload weapons, handling rails, storage arrangements, and associated equipment is used instead for fuel, machinery, stores, and surface-combat requirements.
106.25 mm Wet Guns
The UB-20 carries:
2 × 106.25 mm submersible wet deck guns
The guns constitute the submarine's principal weapon for ordinary commerce-raiding operations.
Approximately 500 rounds are carried for the two-gun battery.
The weapons are intended for attacks against merchant vessels, auxiliary ships, exposed shore targets, and other targets that do not justify expenditure of one of the submarine's eight torpedoes.
The mounts are designed to tolerate routine immersion rather than requiring removal or extensive preparation before diving.
Surface gun action nevertheless prevents the submarine from maintaining its normal rapid-diving condition while gun crews are exposed and ammunition is being handled.
A commander who commits to a gun engagement therefore temporarily exchanges the class's primary defensive advantage for greater surface firepower.
12.5 mm Heavy Machine Guns
Close-range defense is provided by:
- 2 × twin 12.5 mm heavy machine-gun mounts
The weapons serve two related purposes.
They provide limited close-range anti-aircraft defense during periods when immediate diving is impossible and provide heavy close-range fire against small craft or personnel attempting to approach or board the submarine.
The weapons are not intended to encourage prolonged combat with aircraft.
If immediate submergence remains possible, diving is the preferred defense.
Sensors and Fire Control
The UB-20 carries passive hydrophones for underwater detection and local situational awareness.
The system represents contemporary passive acoustic technology and is principally useful for detecting nearby propeller and machinery noise.
The class carries no active acoustic ranging system.
Two periscopes support submerged operation:
- Attack periscope
- Observation/navigation periscope
Torpedo attacks rely upon visual observation, manual plotting, estimated target course and speed, mechanical calculating aids, and gyro-angle settings.
The class predates the highly integrated electromechanical torpedo fire-control systems used by later Gondaran submarines.
Wireless telegraph and radio receiving equipment provide long-range communication when surfaced.
Operational Doctrine
The UB-20 is designed as a long-range surface raider.
Strategic transit is normally conducted on the surface, where the submarine can exploit its powerful diesel machinery and unusually high useful cruising speed.
Its preferred operational pattern is:
- Transit rapidly to a patrol area.
- Search primarily while surfaced.
- Identify vulnerable shipping, isolated support vessels, or weakly defended routes.
- Use surface gunfire against targets that can be attacked economically.
- Use torpedoes against dangerous, valuable, or tactically unsuitable targets.
- Submerge for concealed attack or when threatened by superior forces.
- Evade immediate pursuit.
- Return to the surface when conditions permit.
- Relocate before enemy patrol forces can concentrate.
The submarine is not intended to remain in an area after enemy strength has become concentrated.
Gondaran raiding doctrine treats strategic maneuver as a weapon.
A UB-20 that forces an opponent to send destroyers, aircraft, escorts, and patrol vessels into one area has already altered the enemy's deployment.
The Gondaran commander is then expected to exploit the resulting weakness elsewhere rather than remain and fight the concentrated response.
High sustained cruising speed allows the submarine to shift between distant operating areas more rapidly than an opponent expecting conventional economical submarine transit.
This makes the UB-20 particularly suited to the geographic scale of the Pacific.
Surface Combat
Surface gunfire remains a normal component of UB-20 operations.
The submarine is expected to use its 106.25 mm battery when conditions permit a target to be destroyed without expending a torpedo.
This distinguishes the class sharply from later Gondaran submarines.
Surface engagement remains subordinate to survival. A UB-20 commander is not expected to duel an enemy warship merely because the submarine carries two substantial guns.
If the enemy possesses superior firepower or an effective anti-submarine response is developing, the submarine is expected to break contact.
Underwater Combat
Submerged operation is tactical rather than strategic.
The six forward torpedo tubes permit a heavy concealed attack, while the stern tubes provide additional flexibility during withdrawal.
The submarine's low submerged speed means that it cannot easily recover a poor underwater tactical position through speed alone.
A successful commander therefore relies upon preparation, positioning, surprise, and rapid return to surface mobility once the immediate threat has passed.
Evolution of Gondaran Submarine Doctrine
The UB-20 establishes several characteristics that remain visible throughout later Gondaran submarine development.
Its emphasis on useful strategic cruising speed becomes a central feature of the UB-30.
Its rapid-diving requirement establishes crash diving as a major Gondaran submarine specialty.
Its heavy surface armament, however, reflects a doctrine that would gradually disappear.
The evolutionary sequence is:
- UB-20 — surface raider that submerges.
- UB-30 — balanced traditional ocean-going submarine.
- UB-40 — underwater-oriented torpedo submarine.
The UB-30 retains the surface mobility and rapid-diving principles of the UB-20 while substantially increasing torpedo endurance and reducing the importance of surface gun combat.
Later designs shift progressively greater engineering effort toward submerged mobility, underwater endurance, and torpedo warfare.
The UB-20 therefore represents the beginning of a continuous Gondaran design lineage rather than an isolated experimental type.
It demonstrates the central principle that would remain common to later Gondaran raiders:
- A vessel does not need to be superior in every characteristic.
- It must be exceptional in the characteristics required to perform its intended mission.