To answer this, we have to go back to the first British naval mission in Greece, under Vice Admiral Tufnell. The aim of the naval mission, established in 1910, was to re-organise the Greek Navy, to supervise and improve training and logistics, and to guide Greek naval procurement towards British yards. Tufnell had encountered several obstacles in carrying out these objectives to his full satisfaction. In May 1913, when the contract for the first mission was up, the Greeks requested that Tufnell and much of his mission be replaced with officers from the active duty list. Rear Admiral Kerr was chosen for this duty. There were several reasons for this - he was a close friend of the First Sea Lord, Prince Louis of Battenberg, and by extension the Royal Family, he was an able professional officer, whom Admiral Fisher described as 'the ablest captain on the Navy List', and he had previously been a naval attache in Greece in 1903-4. Kerr would be joined by 18 other officers, to join the two that had remained from Tufnell's mission.

The British Admiralty had been disappointed at the obstacles faced by Tufnell. Part of these had come from his status, and it was hoped that Kerr, with his royal and professional connections would avoid these. But to ensure that all other obstacles were swept aside, they insisted that the mission was invested with 'full and effective control' by the Greeks. This had been echoed by the remaining members of the Tufnell mission, who had asked the Greek Government that the new contract for the mission include supervision over all branches of the Navy, along with full control over promotions, appointments, recruitment and training. The Greeks made a counteroffer, which gave members of the mission administrative authority conforming to a decree passed in August 1912 concerning inspections. However, Tufnell felt that this decree, rather than expanding the mission's powers, had been passed to limit them. The British counteroffer suggested that the officers of the mission be granted Greek commissions, for the rank they were to hold in the Greek navy - this way, the British would get the authority they wanted, while the Greeks would effectively retain their sovereignty. By August 1913, the contract for the new mission was ready. While the mission did have to stick to the August 1912 decree limiting their powers, they were also commissioned into the Greek Navy, and were able to hold commands in any squadron or department, with the exception of the Ministry of Marine. The mission had no direct power over appointments, but were required to be consulted before anything could happen. In the event of war, the officers of the mission were not to take any active role, but were to maintain an advisory position. A large amount of power over the Greek Navy was invested in Kerr: he was a member of all committees of the Ministry of Marine, he had access to all confidential reports, he could issue movement orders to any unit of the fleet, and could take preparatory steps towards procuring new material (in addition to his vote on the Committee of Naval Construction). He could also issue orders to any member of the mission. These had a variety of roles, mainly in training and inspection - British officers headed the main training centres for gunnery, torpedoes and officers, while others had inspection powers over aviation, submarines, dockyards and construction, and marine engineering.

The Kerr mission had several major effects on the Greek Navy in the run-up to WW1. They helped develop the naval Boys School in Poros, an important source for enlisted men. They improved naval logistics, creating a supply dump in Piraeus, and removing corruption within the system. They helped the enlisted, increasing wages, reducing punishments, and establishing canteens aboard ships. They oversaw a great expansion of the Naval Staff, and the Naval Air Service. Naval training was reorganised along British lines, and several British manuals, for things like minesweeping, were introduced. Kerr also attempted to persuade the Greek Navy to move away from capital ships, and towards large flotillas of destroyers and cruisers, to mixed results.

However, their effects on Anglo-Greek naval strategy are somewhat more complex. Under Tufnell, the mission had been trying to draw Britain and Greece together, as anchorages in the Ionian islands would be advantageous for Britain in a war against Austria-Hungary. Alliance with Greece would also help to swing other Mediterranean nations, such as Spain, towards the Entente. However, 1913 brought several changes to the situation which weakened the allure of an Anglo-Greek alliance. The Germans accepted British proposals to reduce the pace of construction. The Austro-Hungarian parliament decided not to build another squadron of dreadnoughts. Windfalls from taxation and from the colony of Malaya meant that the Admiralty could easily build more capital ships without having to ask for higher taxes. All this meant that the British position in the Mediterranean became stronger, as the threat in the North Sea decreased. Meanwhile political developments - mainly the accession to the throne of the pro-German Prince Constantine, but also suggestions that an Anglo-Greek alliance would tighten bonds between Austria and Italy discouraged Britain from alliance with Greece. Meanwhile, the rise of Russia made the Ottoman Empire somewhat more of a tempting target, and an alliance with Greece would only antagonise them. As such, from this point to the start of WW1, the mission concerned itself solely with training and construction. However, Kerr had developed a strong attachment to Greece, and in December 1913 was a strong proponent of assisting them against Turkey over the Aegean islands. Once the war, things became somewhat more complex, due to the complex political schism within Greece. King Constantine was strongly pro-German, but his PM, Eleftherios Venizelos, was strongly pro-Entente. The British were still hoping to keep the Ottoman Empire out of the war, which an alliance with Greece would have greatly jeopardised. As a result, Kerr initially swung his support behind Constantine, supporting his position in council and elsewhere. He helped Constantine draft a statement to the Entente, stating that Greece would not fight Turkey unless attacked. However, he tempered this, reminding Constantine that if Greece was too friendly to the Central Powers, the RN and French Navy could wipe Greece off the map. However, following the Ottoman entry to the war, he swung to Venizelos. Kerr may have had some minor part in the Ottoman entry to the war, which was essentially occasioned by the arrival of the German warships Goeben and Breslau at Constantinople. There is evidence that Kerr knew where they were heading, as he had been informed of German intentions by Constantine, but failed to pass this to London in time for action to be taken. Through his support for Venizelos, Kerr helped gain permission for an Anglo-French force to land at Salonika to aid the Serbs.

Kerr remained in Greece until September 1915. In March 1915, he had developed rheumatism, which by May had become bad enough that he requested permission to return home to recuperate. He was granted temporary leave at the end of the summer, but would never return. With him gone, the naval mission somewhat collapsed. The Greek admirals began to reassert their control over the Greek Navy. In 1917, with Greece fully under the control of Venizelos rather than the monarchy, the Greeks requested another naval mission. However, Admiral Coundouriotes, the Greek C-in-C, would not allow himself to be superseded by a British officer, so Captain Clifton Brown was chosen to lead it. Brown's mission arrived in December 1917, but would leave in 1919, thanks to accusations of meddling with Greek politics. There were five more British missions in the period from 1919 to 1932, as well as several more following WW2. The British had very little impact on the Greek Army. There was a French military mission to Greece which would have had a greater effect on the Army, but I know very little about it.

Sources:

Greek Naval Strategy and Policy 1910-1919, Zisis Fotakis, Routledge, 2005

Greece and the Allies, 1914-22, G. F. Abbott, Methuen, 1922

Superior Force, Geoffrey Miller, University of Hull Press, 1996