It was not, per se., the Royal Navy that led tank development; rather, it was the Royal Navy Air Service (RNAS). The RNAS developed an armoured car force in the early years of WWI; the experience developed from this helped put it at the forefront of British AFV development. The RNAS was able to develop these capabilities because it had a large budget that operated outside the constraints that were placed on the rest of the RN, in addition to the military needs for them.

An RNAS wing, under the command of Commander Charles Samson, deployed to France and Belgium in August 1914, to support the operations of the Royal Marine Brigade at Ostend. Part of this role involved providing reconnaissance support for the Brigade. The RNAS had brought several civilian cars to the front with them; ten touring cars, two lorries, and eight buses. The cars were to be used to find new airfields, to carry mechanics and spare parts (that could not be carried by airplane) to those airfields, and to locate aircraft and pilots that had been forced down behind, or close to, British lines. However, a lack of aircraft forced the cars into action. On the 29th August 1914, General Aston, commanding the Marine Brigade, asked Samson to use his cars to reconnoitre the towns of Thourout and Bruges. Two cars were chosen, one armed with a machine gun, and the other acting as a personnel carrier. The reconnaissance was carried out without incident, but proved the utility of cars in modern warfare. Samson began to take steps to use them more widely. Car patrols were instituted behind British lines to support any downed pilots. Other cars were given improvised armour and armaments, and used to patrol in front of British lines.

On the 4th September, the first engagement between Samson's cars and German forces took place. Samson received reports that German cars had been seen passing through Armentieres, and planned an ambush at a bend in the road along their likely route. While the German cars reached the ambush site before Samson's cars did, the British drove them off with machine gun and rifle fire - though the machine gun would jam after just forty rounds. Shortly afterwards, one of the trucks was converted into an armoured car; it received a 3 pdr gun and a light machine gun, with armour to protect the engine, driver and gun crew. Based on these experiences, Samson called for more armoured cars to be constructed and for more men to be sent to him for armoured car operations. Winston Churchill, First Lord of the Admiralty (civilian head of the RN), took a keen interest in the RNAS' new capability. He formed the Armoured Car Division as a subsidiary unit of the RNAS. In mid-September, the first purpose-built armoured cars began to arrive in France. They were well-protected, but this did not extend to the gunners, who were exposed; this meant that they were not very popular. Two armoured car squadrons were formed, one under a Major Risk of the Royal Marines, and another under Lord Annesley. Annesley had armoured his own car in a local garage. While this enthusiasm was encouraging, the armour was only soft iron, which could not stop bullets, and it had not been well attached, tending to drop off at inopportune moments. Despite a number of unkind jokes, Annesley persevered, and became seen as a capable, indispensable officer. On the 1st October, a third squadron of improvised cars arrived. A few days later, the RNAS wing moved forward to Antwerp. It did so in an impressive convoy of motor vehicles; seventy buses, escorted by 11 armoured cars, six with machine guns, and two armoured lorries. At this time, the RNAS also operated three armoured trains, though one was manned mainly by Belgian personnel.

In December 1914, an armoured car squadron was formed to patrol the east coast of the UK against German raids. A month later, there were eight 12-car squadrons in commission, though some squadrons had not received machine guns for their cars. By March 1915, the RNAS armoured car force had grown into a full division. The division was intended to consist of fifteen squadrons, each squadron consisting of three four-car sections. Each squadron would also receive three armoured trucks armed with 3pdr guns, and a number of unarmoured cars and trucks for logistics and communications duties. In the end, however, five squadrons would not receive armoured cars, but rather machine-gun armed motorcycle and sidecar combinations. The typical RNAS armoured car was built on a Rolls Royce or Lanchester chassis. It had an armoured body, with a machine gun mounted in a rotating turret. In March 1915, 78 Rolls Royce cars, 36 Lanchester cars and 3 Talbot cars had been converted to armoured cars. As the fronts bogged down in France, RNAS armoured cars were sent elsewhere. Two squadrons took part in the Gallipoli Campaign, before being moved to the Sinai front. A third was deployed to South-West Africa, to roll up the German colony there. A fourth participated in the East African campaign. In August 1915, the armoured car division was disbanded, with the exception of Number 1 Squadron. The cars were handed over to the Army. Number 1 Squadron remained in Flanders until October 1915, when it was sent to Russia. It operated there until mid-1917, when it returned to the UK following the failure of the Kerensky Offensive. On its return, it would be disbanded, and its cars returned to the Army.

Tanks developed from an idea Churchill had in January 1915 for some kind of machine to break the deadlock on the Western Front. He sent a note to the head of the RNAS, Captain Murray Sueter, which proposed using steamrollers to crush German trenches. Churchill saw the RNAS as his own personal fiefdom, as it was separated bureaucratically from the rest of the Admiralty. It also had its own independent budget, from which money could be diverted to Churchill's pet projects. Sueter referred Churchill's madcap idea to Lieutenant Barry, who was in charge of armoured car development. Barry pointed out that a steamroller was precisely the wrong thing for the purposes for which Churchill was suggesting they be put. A steamroller had too much ground pressure to cross no-man's-land without sinking in. Instead, Barry suggested using the American Holt tractor, a vehicle with caterpillar tracks, which would spread the weight of the vehicle across a large area, preventing it sinking. Sueter procured a Diplock caterpillar truck, and, on the 16th February, showed this off to Churchill on Horse Guards Parade. Sueter and Churchill almost immediately saw the possibilities for the new concept; adapting the standard armoured car body to use tracks rather than a wheeled chassis would be highly useful.

To carry this project forwards, Sueter introduced Eustace Tennyson D'Eyncourt, the Director of Naval Construction, to the scheme. While this might seem like a strange choice, the DNC's department had been responsible for procuring the armour plate for the armoured cars. Shortly afterwards, the Fourth Sea Lord ordered Sueter to stop messing around with armoured cars, and to concentrate on the RNAS's main role. As such, D'Eyncourt took charge, though it remained mainly under the control of the RNAS. A Landship Committee was formed, with D'Eyncourt, Squadron Leader Hethrington of the RNAS and Colonel Dumble of the Naval Brigade. The Committee purchased a Killen-Strait tractor from the USA, shipping it to the UK. On the 30th June 1915, it was demonstrated at the Naval Air Station at Wormwood Scrubs. Hethrington drove it over a specially prepared obstacle course, in front of a number of dignitaries, including David Lloyd George. Sueter wished to absorb the new 'landships' into the RNAS' armoured car organisation. Number 20 Squadron was formed to operate them. However, Churchill, the main sponsor of the RN's involvement in the project, was removed from his post following the initial failures of the Gallipoli Campaign. The new Board of the Admiralty was less enthusiastic about these weapons, useful only for fighting on land. They handed the project, and some of the personnel involved, over to the War Office, who saw it to fruition.