British ex-pats in this area of Spain sometimes call these weapons the “Guns of Mazarone,” not only failing to use the official name but also using some poetic license to mispronounce the name of the nearby town, Mazarrón to make a rhyme with “Navarone.” The comparison is not without a little justification.
The gun battery was built to prevent enemy ships entering the bay to attack the important port and military arsenal at Cartagena. You really seem to be very high above the sea at Castillitos, though the actual altitude is only about 800 feet.
The Bateria de Castillitos military buildings are extensive and were built in an ornate, crenelated style reminiscent of a Disney set. You can look inside a many of them including both the gun control bunkers and many of the crenelated towers. The highlights of the visit, however, are the massive 381mm guns with the 17m long barrels each mounted in an enormous turret.
These guns were only ever fired once in action. This was during the Spanish Civil War by the Republican Forces against Franco’s Nationalist fleet in April 1937 (Cartagena was a strongly republican stronghold). After being demonstrated once it is unsurprising that these guns, that could fire a one-ton projectile over 35 miles, were not called upon to be used again.
These, and several other, gun batteries overlooking the bay (the Bateria del Jorel,with its slightly smaller guns, is also worth a visit and has to be reached on foot further along the headland) were only taken out of service in 1994 but, given the advancement in naval offensive armaments since WW2, they would probably been little more than symbolic for many years. They were manufactured by the Vickers company in the UK in 1927 and 1928. Apparently these massive gun barrels were towed up the steep winding road by steam traction engines. After driving up there in a modern car the mind boggles at the prospect. Even the prospect of transporting numerous one ton shells up there is amazing.
After taking a good look at the guns and the military buildings it will then become clear that even without these features many people would be prepared to drive the long and winding (and obviously easily defended) route along that narrow road just to see the views (parking is reasonably plentiful and turning round is not a problem). Looking roughly west you stare out over shimmering waters of the Bay of Mazarrón in the opposite direction to look over Cartagena's huge bay. On a sunny day there can be no better coastal views in Spain.