Machine gun armed armoured cars were deployed throughout World War One, by most of the major powers. The Belgians were the first to effectively employ armoured cars, deploying Minerva Armoured Cars during the German invasion. The British Royal Naval Air Service (RNAS) also deployed armoured cars. The initial RNAS deployment to Belgium had included a section of unarmed, unarmoured cars for patrolling supply lines and recovering downed pilots. These were swiftly armed and armoured with scavenged equipment. On the 4th of September 1914, one of these cars, armed with a Maxim MG, destroyed a German car near Cassel, proving the concept. The officer in charge, Commander Charles Samson, swiftly had a shipbuilder in Dunkirk add armour to his cars. They would go on to fight in several skirmishes in Belgium and Northern France in September and October. Meanwhile, the RN and Rolls Royce were developing a new armoured car, with the first models arriving from October. The RNAS formed a strong force of armoured cars, and by November had formed the Royal Naval Armoured Car Division. As the Western Front settled into trench warfare, for which the cars were unsuitable, the RNACD began to serve elsewhere. Three squadrons were sent to aid the Russians - photos from this operation can be found here, with this one showing what the cars looked like. Other squadrons served in Romania, the Middle East, and at Gallipoli, though for the latter, they dismounted their MGs.

The Royal Naval Air Service Armoured Car Division was a small unit used from at least September/October 1914 for rescuing downed pilots, reconnaissance and combat duties. They had armoured Rolls Royce cars armed with Maxim guns and a truck with a small artillery gun, among other things.

Source; Perett, Bryan: 'Iron Fist: Classic armoured warfare case studies', Arms and armour press, 1999.