HMS K26 was the only modified K-class

British K class submarine

The K class submarines were a class of steam-propelled submarines of the Royal Navy designed in 1913. Intended as large, fast vessels which had the endurance and speed to operate with the battle fleet, they gained notoriety, and the nickname of Kalamity class, for being involved in many accidents....

 submarine

Submarine

A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...

 of Britain

United Kingdom

The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

's Royal Navy

Royal Navy

The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...

 to be completed. One of six ordered, she was laid down towards the end of the First World War but not completed until five years after its end.

Six boats, K23-K28 were ordered in June 1918 but the end of the war meant that only K26 was completed, the remainder all being cancelled on 26 November 1918. Even so, she was finished slowly. Although launched at Vickers yard in August 1919 she was towed to Chatham

Chatham Dockyard

Chatham Dockyard, located on the River Medway and of which two-thirds is in Gillingham and one third in Chatham, Kent, England, came into existence at the time when, following the Reformation, relations with the Catholic countries of Europe had worsened, leading to a requirement for additional...

 in 1920 and completed in June 1923.

She was a better design than the previous seventeen K-boats, experience with them having led to various changes. The swan bow was modified and the hydroplanes moved to operate in the wake of the propeller

Propeller

A propeller is a type of fan that transmits power by converting rotational motion into thrust. A pressure difference is produced between the forward and rear surfaces of the airfoil-shaped blade, and a fluid is accelerated behind the blade. Propeller dynamics can be modeled by both Bernoulli's...

s. All of this led to a reduction in speed of around 0.5 knots (0.9 km/h) on the surface compared to her predecessors.

She also had six 21 inch (533 mm) torpedo tubes in the bow instead of the four 18 inch (457 mm) ones of the earlier members of the class, which required her to be 12 feet (4 m) longer. The four 18 inch (457 mm) beam tubes were nevertheless retained. The superstructure was modified to improve the protection of the funnel

Funnel

A funnel is a pipe with a wide, often conical mouth and a narrow stem. It is used to channel liquid or fine-grained substances into containers with a small opening. Without a funnel, spillage would occur....

s and uptakes, and almost cured the unfortunate tendency of water entering down the funnels putting the boiler

Boiler

A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications.-Materials:...

 fires out in bad weather

Weather

Weather is the state of the atmosphere, to the degree that it is hot or cold, wet or dry, calm or stormy, clear or cloudy. Most weather phenomena occur in the troposphere, just below the stratosphere. Weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate...

.

She also had capacity for 300 tons of fuel oil, instead of the 197 tons of the earlier boats which gave her a greater range even though her displacement was larger. Underwater endurance was similar to her predecessors. Improved ballast tank arrangements cut the diving time to 3 minutes 12 seconds to get to 80 feet (24 m). She also had an increased maximum diving depth of 250 feet (76 m).

In 1924 she embarked with much publicity on a long voyage via Gibraltar

Gibraltar

Gibraltar is a British overseas territory located on the southern end of the Iberian Peninsula at the entrance of the Mediterranean. A peninsula with an area of , it has a northern border with Andalusia, Spain. The Rock of Gibraltar is the major landmark of the region...

, Malta

Malta

Malta , officially known as the Republic of Malta , is a Southern European country consisting of an archipelago situated in the centre of the Mediterranean, south of Sicily, east of Tunisia and north of Libya, with Gibraltar to the west and Alexandria to the east.Malta covers just over in...

 and the Suez Canal

Suez Canal

The Suez Canal , also known by the nickname "The Highway to India", is an artificial sea-level waterway in Egypt, connecting the Mediterranean Sea and the Red Sea. Opened in November 1869 after 10 years of construction work, it allows water transportation between Europe and Asia without navigation...

, to Colombo

Colombo

Colombo is the largest city of Sri Lanka. It is located on the west coast of the island and adjacent to Sri Jayawardenapura Kotte, the capital of Sri Lanka. Colombo is often referred to as the capital of the country, since Sri Jayawardenapura Kotte is a satellite city of Colombo...

 and Singapore

Singapore

Singapore , officially the Republic of Singapore, is a Southeast Asian city-state off the southern tip of the Malay Peninsula, north of the equator. An island country made up of 63 islands, it is separated from Malaysia by the Straits of Johor to its north and from Indonesia's Riau Islands by the...

 and back again.

She was taken out of service in April 1931 because her displacement exceeded the limits for submarine displacement in the London Naval Treaty

London Naval Treaty

The London Naval Treaty was an agreement between the United Kingdom, the Empire of Japan, France, Italy and the United States, signed on April 22, 1930, which regulated submarine warfare and limited naval shipbuilding. Ratifications were exchanged in London on October 27, 1930, and the treaty went...

 of 1930, and broken up shortly afterwards.
She was the last steam-powered submarine built anywhere in the world until the first nuclear power

Nuclear power

Nuclear power is the use of sustained nuclear fission to generate heat and electricity. Nuclear power plants provide about 6% of the world's energy and 13–14% of the world's electricity, with the U.S., France, and Japan together accounting for about 50% of nuclear generated electricity...

ed submarine, was launched in 1954.