Checked my notes and this is what I found:

A description is found in Kelshall, Gaylord T. M. 1994 The U-Boat War in the Caribbean United States Naval Institute Annapolis Maryland ISBN: 1557504520

My notes on the matter read in part:

“It was within that context that the Cuban Navy participated in the Battle of the Caribbean . When Cuba entered the modern war, its Navy only had a few old and inefficient vessels.

At the end of December, 1941, and the beginning of 1942, several agreements were signed between the governments of the US and several Latin American and Caribbean countries, including Cuba .

Those agreements aimed at strengthening the defensive potential of Latin America and the Caribbean while, in reciprocity, they should continue to provide the required raw materials for the US military industry.

Due to Cuba 's strategic location, recognized historically as the Key to the Gulf of Mexico and the center of the maritime routes that cross the Caribbean Sea, it was of great interest to the US that the Cuban Navy participate in the Battle of the Caribbean escorting the freighter convoys and patrols in the surrounding waters.

Thus, the old cruiser Cuba , which was the largest Cuban warship, and the school-ship Patria were sent to the shipyard in Galveston , Texas , where they were totally transformed and modernized. These works took almost a year.

Also, the gunboats Baire, Yara, Juan Bruno Zayas, Pinar del Rio, 4 de Septiembre, Matanzas, Santa Clara, Camagüey, Oriente and Donativo , as well as the auxiliary vessels BA-1, BA-2, BA-3, BA-4 BA-5, BA-6 and BA-7 were modernized in Cuban and US shipyards.

As part of these agreements, the US established an Air Base in San Antonio de los Baños, 20 kilometers South of Havana, and another one in San Julian near the Western tip of Cuba. In addition, they built a landing field in Camagüey, a zeppelin base in Caibarien, and another one in the Isle of Pines .

The main target for all of these installations was the struggle against the submarines.

Another step was to provide the merchant marine vessels of the allied nations, including Cuba , with artillery. In many cases, US personnel operated the artillery on the merchant ships.

At the same time, through the Law of Loans and Leasing enacted by the US Administration, 12 leased patrol craft were transferred to the Cuban Navy, forming a fleet of 4 squadrons and 3 units each. The crew for these vessels received a three-month training course in several bases and training centers in the US .

The patrol craft fleet began operations in April, 1943. It was assigned to escort the merchant vessels that moved between Cuban ports and, one of the squadrons, escorted the daily Seatrain ferry that operated between Havana and Florida ports.

The efficacy of the fleet was soon described as outstanding. US Senator Kenneth McKellar, referring to the fleet's performance during the first trimester of operations, expressed before the US Congress:

“The Patrol Craft Fleet of the Cuban Navy, during this period (April, May and June, 1943), has had a loss of only 0,027% T, while convoying during enemy attacks and one of the patrol craft has had an outstanding success. The operation of these units of the Cuban Navy had prevented the US Navy from using a considerable number of its Navy personnel for those same purposes.”

The outstanding success -which was also the greatest one achieved by the small Cuban Navy- was the sinking of a German submarine in the Old Bahamas Canal, not far from Cuba's Northern coast.

[www.cubanow.net] Sunk a German Submarine in WWII (Part II) By Cervera Cubanow.-

Gustavo Placer Cervera, a former Commander in Cuba’s Revolutionary Navy, has a Ph.D. in History and has done extensive research in naval wartime operations and written several books.

On May 15, 1943 a squadron of Cuban patrol craft, formed by the CS-11, CS-12 and CS-13, navigated from Isabela de Sagua toward Havana escorting the merchant vessels Wanks (from Honduras) and Camagüey (from Cuba), both loaded with sugar.

The crews of the merchant ships, as well as those of the warships were on full alert. Just before their departure, a warning had been received that a surfacing submarine had been detected off the northern coast of Matanzas .

The merchant vessels sailed in forward lines 500 yards apart. The Camagüey was on the flank nearest to the coast. The escort navigated at a distance of 750-1000 yards. The CS-12 was in front, followed by the CS-11 with the squadron chief on board and, finally, the CS-13 was at the rear guard.

At 5:15 pm , when the convoy navigated at 8 knots off of Cayo Megano, a US mono-motor hydroplane, type OS2U Kingfisher, appeared in the sky coming from the Northeast. The plane went into a nosedive and, flying at low altitude, circled twice, swaying, and turning on and off its engine.

According to an established code, these maneuvers were used to announce the presence of a German submarine. To show the exact position, the plane dropped a gas bomb.

Then the squadron chief of the patrol craft ordered the commander of the CS-13, Second Lieutenant Mario Ramirez Delgado, to explore the area pointed out by the plane. After this incident, he continued in Cuban Navy until 1952. In January of 1959, he resumed his services in the Cuban Navy until 1962, when he transferred to the Merchant Marine.

I still remember him as Lieutenant Commander of the Merchant Navy, with a vibrant voice, when he addressed the students and professors at the Naval Academy formed for a review that I helped organize honoring the 40 th anniversary of his deed and in remembrance of the Cuban seamen who died during World War II. Mario Ramirez Delgado died in Havana at the end of the 80s. Before passing away, h e told me what actually happened that day.
Once the order was received, the CS-13 sailed speedily toward the area, where the patrol boat’s hydro-acoustic means of detection received a clear and precise contact at 900 yards: it was the submarine maneuvering to escape.

The seaman operating the sonar, Norberto Collado Abreu, was glued to the equipment, without missing a sound. Then the attack started: three deep charges set to explode at 100, 150 and 250 feet were dropped from the stern, in accordance with the calculated immersion speed of the submarine.

Four explosions were clearly detected. The fourth explosion was so strong that the stern of the Cuban patrol boat was submerged and water came in through the hatchway of the engine room.

At that time the hydrophones reported a sound similar to a liquid bubbling when it comes from a submerged container that is suddenly opened. Its intense whistling slowly decreased. These sounds indicated that the submarine had been hit.

To finish off, the patrol boat launched two more deep charges, set to explode at 250 feet. A few minutes later, a dark stain was observed on the water surface. A spurt of a black and viscous substance smelling like gasoline came from the deep. According to Ramirez, he ordered to take a sample of the substance as proof of the sinking of the enemy submarine.

Thirteen years later, Norberto Collado Abreu, the efficient sonar operator, had a transcendental appointment with Cuban history: he was the helmsman of the Granma yacht in its historical 1958 crossing.

At the present time, more than 80 years old, he is still an active Lieutenant Commander in charge of the Granma yacht at Havana ’s Museum of the Revolution.

The exploration of the area with the hydro-acoustic equipment continued shortly after, but no sound was detected. The patrol boat then joined the convoy again and continued its crossing. Upon arrival in Havana and after personally informing the Head of the Navy, the CS-13 Commander talked on the phone with the President (Fulgencio Batista), who ordered him to keep absolute silence about what had happened. The incongruity of this order was manifested that same night when the station of the US Naval Base broadcasted the news of the encounter and possible sinking of a German submarine. London ’s BBC also broadcasted the news. Some authors have speculated about a possible smuggling of gas and provisions with the German submarines, but there has been no proof to that respect.

For some unknown reason the sinking of the German U-176 remained a secret to the Cuban public opinion until after the end of the war, according to Mario Ramirez Delgado.

When World War II ended and the files of the German Navy were seized, it was confirmed that the submarine which was operating in that area and whose contact had been lost in those days was the U-176 commanded by Kapitänleutenant Reiner Dierksen. This submarine had sunken 11 ships for a total of 53,307 T.

Information available through Internet has allowed us to determine that the sunken submarine was of the IX-C type: 76, 8 m length, 6, 8 m beam, 4, 7 depth and 9, 4 m depth of hold. Its total displacement was 1,540 T, 1,120 on the surface and 1,232 submerged. They reached a speed of 18, 3 knots on the surface and 7, 3 submerged, and had 6 torpedo-launching tubes (4 in the bow, 2 in the stern) and carried 22 torpedoes. They also had a 105 mm. cannon and another one of 45 mm. Their engines had 4,400 HP on the surface and 1,000 HP submerged. Their operating range reached 13,450 miles. The U-176 had been launched at the AG Wesser shipyards in Bremen on February 6, 1941 .

In 1946, Mario Ramirez Delgado, already promoted to Lieutenant, was awarded the Navy Merit Medal with a red distinctive. Rear Admiral Samuel E. Morison, official historian of the US Navy, recognized his success in his work History of US Naval Operations in World War II, where he also praised the ability and efficiency of the Cuban seamen.

“…The CS-13 patrol boat, commanded by Second Lieutenant Mario Ramirez Delgado, turned toward the gas, made good contact through the sonar and launched two perfect attacks with deep charges which annihilated the U-176. This was the only successful attack against a submarine done by a surface unit smaller than a PCE of 180 feet, thus, the sinking is properly considered with great pride by the small but efficient Cuban Navy.”

The year 1943 marked the end of the Battle of the Atlantic and, therefore, of the Caribbean . During that year the improvement of the anti-submarine forces and means decreased the sinking of transport ships and increased the destruction of enemy submarines.

During the spring of that year, the German submarine fleet made an enormous effort by having almost 400 units operating in the Atlantic. During the first three weeks of March, the losses of merchant ships reached 750,000 T. But later, they began to decrease rapidly. The submarine offensive started to loose strength while the anti-submarine forces grew dramatically.

In May 1943, 42 German submarines were sunken and, during the whole year, the losses in the Atlantic reached 237. What was even worse for them was that they had lost their best crews and commanders.

In spite of this, the German submarines were still a danger in Cuban waters. During 1943, two Cuban and one American merchant ships were sunk in waters off of Cuba . In February 1944, when the outcome of the Battle of the Caribbean was defined and the anti-submarines forces were dramatically superior in the region, the German submarines were still able to sink several ships, among them two Cuban merchant ships.

During the war, the Cuban Navy surface units rendered their services as escort of merchant ships in Cuban waters and on the routes between Havana and Florida ports. The total amount of escorted ships was 414, which amounted to 2,268,680 T. The losses were 0.19% of the tonnage.

While rendering several services, the Cuban Navy vessels navigated 399,755 miles (134,206 in convoy escorts; 66,778 in patrols; and 12,032 in aid services: they rescued 221 shipwrecked persons).

The cruiser Cuba , the biggest of the Cuban ships, navigated during the war 27,974 miles and escorted 89 allied merchant ships with a total displacement of 712,000 T. The school-ship Patria sailed 21,178 miles and escorted 70 merchant ships with a displacement of 450 000 T.

The Cuban Navy Aviation escorted during World War II 114 vessels for a total of 500,000 T., flying 83,000 miles rendering services as convoy and patrol without loosing any ship to the enemy.

The above-mentioned Rear Admiral Morison said to that respect: “ Cuba was, with the exception of Canada , our most useful ally in North America ; its fleet of small gunboats was in charge of the coastal traffic and collaborated escorting the ferries between Florida and Havana …”

Due to the favorable conditions created by the action of the Cuban naval forces during 1944, 39 Cuban ports registered 5,655 entries of vessels, of which 2,670 were Cuban ships and 5,602 departures, of which 2,117 were Cuban.

During the war, the tiny Cuban merchant marine lost six ships, amounting to 10,296 T., which represented 17, 44% of its total tonnage, and 79 Cuban seamen lost their lives in the sinkings by German submarines. There is a monument located at Havana ’s Avenida del Puerto in their honor.

US Senator McKellar had said in his speech (mentioned in Part I): “The Cuban seamen have behaved as steel men on wooden ships.” “