The British Isles required four oil tankers of petroleum daily during the early war years, and most of it came from Venezuela, through Curaçao, after Italy blocked passage through the Mediterranean Sea from the Middle East.

The southern United States Gulf of Mexico coastline, including petroleum facilities and Mississippi River trade, could be defended at two points.

[2] United States Navy VP-51 Consolidated PBY Catalinas began neutrality patrols along the Lesser Antillies from San Juan, Puerto Rico, on 13 September 1939.

[3] The United Kingdom had established military bases on Trinidad; and British troops occupied Aruba, Curaçao and Bonaire soon after the Netherlands were captured by Nazi Germany.

The French island of Martinique was perceived as a possible base for Axis ships as British relationships with Vichy France deteriorated following the Second Armistice at Compiègne.

[4] Declaration of war on 8 December 1941 removed United States neutrality assertions which had previously protected trade shipping in the Western Atlantic.

The relatively ineffective anti-submarine warfare (ASW) measures along the United States Atlantic coast observed by U-boats participating in Operation Paukenschlag encouraged utilizing the range of German Type IX submarines to explore conditions in what had previously been the southern portion of a declared Pan American neutrality zone.

These eleven submarines would patrol independently to disperse Allied ASW resources until exhaustion of food, fuel or torpedoes required them to return to France.

Following the attack, U-156 sailed past Oranjestad, 14 miles to the west, and fired three torpedoes at the Shell tanker Arkansas berthed at the Eagle pier.

At nightfall the crew buried the sailor who died when the gun exploded, and the captain received permission to sail to Martinique, where the injured crewman was put ashore.

In coordination with the attacks on Aruba and Willemstad, U-502 waited to ambush shallow draft Lake Maracaibo crude oil tankers en route to the refineries.

U-161 then left the gulf with decks awash and running lights illuminated to resemble one of the harbor small craft; and then moved off to the northwest before returning to sink a ship outside the Boca.

After sunset on 10 March 1942 U-161 silently entered the shallow, narrow entrance of Castries harbor surfaced on electric motors to torpedo two freighters at dockside; and then raced out under fire from machine guns.

Although results were perceived as less significant, the difficulty of attacks in the Gulf of Paria and Castries by U-161 was comparable to Günther Prien's penetration of Scapa Flow.

The level of success by Italian submarines against a concentration of undefended ships sailing independently was seldom repeated and marked a high point of effective Axis cooperation in the battle of the Atlantic.