Observers were posted to Spanish ports and borders, and both Ribbentrop and Grandi were told to agree to the plan, significant shipments already having taken place. Portugal would not accept observers, although it did agree to personnel attached to the British Embassy in Lisbon. Zones of patrol were assigned to each of the four nations; an International Board was set up to administer the scheme. There were Italian assurances that Italy would not break up non-intervention.
In May, the Committee noted two attacks on the patrol’s ships by Republican aircraft. It iterated calls for the withdrawal of volunteers from Spain, condemned the bombing of open towns, and showed approval of humanitarian work. Germany and Italy said they would withdraw from the Committee, and from the patrols, unless it could be guaranteed there would be no further attacks. Early June saw the return of Germany and Italy to the committee and patrols. Following attacks on the German cruiser Leipzig on 15 and 18 June, Germany and Italy once again withdrew from patrols, but not from the Committee. This prompted the Portuguese government to remove British observers on the Spain–Portugal border. the United Kingdom and France offered to replace Germany and Italy, but the latter powers believed these patrols would be too partial. Germany and Italy requested that land controls be kept, and belligerent rights be given to the Nationalists, so that rights of search could be used by both the Republicans and Nationalists to replace naval patrols. A British plan suggested that naval patrols would be replaced by observers in ports and ships, land control measures would be resumed. Belligerent rights would only be granted when substantial progress was made on volunteer withdrawal.
It culminated in a period during 1937 when all the powers were prepared to give up on non-intervention. By the end of July, the Committee was in deadlock, and the aims of a successful outcome to the Spanish Civil War was looking unlikely. Unrestricted Italian submarine warfare began on 12 August. The British Admiralty believed that a significant control effort was the best solution to attacks on British shipping. It was decided by the Committee that naval patrols did not justify their expense and would be replaced with observers at ports.
The Conference of Nyon was arranged for all parties with a Mediterranean