The United Kingdom and France led the conference, which was also attended by Bulgaria, Egypt, Greece, Romania, Turkey, the Soviet Union and Yugoslavia.

In marked contrast to the actions of the Non-Intervention Committee and the League of Nations, this conference succeeded in preventing attacks by submarines.

[It] preserved the naval status quo in the Mediterranean until the end of the Spanish Civil War: the Francoists received whatever they wanted, the Republicans got very little.

"[1] The Non-Intervention Committee, a group of twenty-four nations set up in 1936 and based in London, had attempted to restrict the flow of weapons to the parties of the Spanish Civil War.

[2] For the United Kingdom, it formed part of the policy of appeasement towards Germany and Italy and aimed at preventing a proxy war – with Italy and Germany supporting Franco's Nationalist Coalition on one side and the Soviet Union supporting the Republican faction on the other – from escalating into a major pan-European conflict.

[4] In May 1937, Neville Chamberlain succeeded Stanley Baldwin as British Prime Minister, and adopted a new policy of dealing directly with Germany and Italy.

[13] Whilst officially being at peace,[13] the Italian leadership had ordered the commencement of unrestricted submarine warfare, referred to in discussion as a campaign of piracy without mention of Italy.

[14] The attack led the British representative in Rome to protest to the Italian Minister of Foreign Affairs, but without response.

[20] British recognition of Italian sovereignty over Abyssinia following the Second Italo-Abyssinian War was an important issue during Anglo-Italian discussions in August 1937.

[22][23] The conference was to be held at Nyon, Switzerland – Geneva was avoided because Italians associated it with the actions of the League of Nations over the Abyssinian Crisis.

[22] On 8 September, plans were discussed in the British Cabinet, including the setting up of eight groups of three destroyers for the western Mediterranean.

Many of the other nations opposed the participation of the Soviet Navy in the Mediterranean,[31] so the United Kingdom and France agreed to handle Aegean Sea patrols.

Signatories were the countries of Bulgaria, Egypt, France, Greece, Romania, Turkey, the United Kingdom, the USSR and Yugoslavia.

[32] The British and French knew that the secret Italian submarine operations had already been paused,[31] but actions to enforce the conference agreement started at midnight on 19/20 September.

Greece and Turkey wanted ships with a clear identifying mark to be excluded, so as to avoid being forced to fire on a German or Italian warship.

[45] The British government, and in particular Neville Chamberlain, desired better relations with Italy and these were achieved with the signing of the Anglo-Italian Agreements of 1938.

He also noted that attacks on submarines would be restricted to suitably extreme circumstances and that the two parties in the war would still not be able to engage neutral vessels.

Christopher Seton-Watson describes it as a "diplomatic victory",[51] but Jill Edwards points out that it failed to achieve a change in Italian policy.

Litvinov, in particular, stressed the Soviet Union's "indisputable right" to commit naval forces to the Mediterranean (something Germany and Italy had opposed in meetings of the Non-Intervention Committee).

He also said he regretted that Spanish merchant shipping had been left out – the other nations believed this would have amounted to formal intervention into the civil war.

[53] Elsewhere, French public opinion was strongly in favour of the outcome of the conference,[50] the only criticism coming from the far left that Republican ships would not receive direct protection.

[41] The Republicans praised the improved safety of the shipping routes, but were somewhat unhappy that belligerent rights had not been granted to both sides.

[36] Italian historians tend to downplay the importance of the Nyon Conference, often seeing it as a mere extension of the Non-Intervention Committee.