Scouting At Sea (1890-2018)
Naval warfare occurs across vast distances and in many cases merely finding the enemy is a complex and critical task. Over the past century, scouting has been performed by a variety of systems from steam cruisers to UAV's. A look at the changes reveals both the early acceptance of naval airpower as well as yet another example of the gradual shift from platforms to systems.
These ships were generally capable of around 20 knots, but their triple expansion engines were unreliable at high speeds and they usually steamed much more slowly. While their lookouts could theoretically see ships out to 15 miles or so and smoke could occasionally be spotted as away as 40 miles, bad weather would reduce this considerably and spotting ships at night was all but impossible (the saying "ships that pass in the night" exists for a reason). Thus, in a 24 hour period a single cruiser could only reliably scout around 4,000 square miles and that figure could easily be cut in half by fog or rain. Further, if something was spotted, a cruiser could only communicate that fact to friendly ships that were within visual range of her signals. This meant that distant scouts were of limited use to the fleet and scouting was more tactical than strategic.
However, a new technology was also appearing - aircraft. While aircraft had revolutionized scouting for ground forces during the war, their impact at sea was much smaller. The low speed and short range of period aircraft (less than 100 knots and usually 2-3 hours respectively) meant that shore based aircraft were of little use to a fleet at sea. However, ship-based aircraft were limited to floatplanes that required their tenders to come to a stop to lower the planes into the water so they could take off or hoist the planes aboard after they had landed.
Despite all of these limitations, aircraft were faster than ships and could see farther. Thus, a single plane could scout around 3,000 square miles during a sortie and it was clear that they would soon become an important asset in naval warfare. The Royal Navy was at the forefront of the revolution, commissioning a dozen seaplane tenders armed with 4-8 floatplanes apiece. Later ships were equipped with a "flying-off deck" forward so that they could launch aircraft on the move. This was then supplemented with a "landing deck" aft, until finally, in the last year of the war, the two were combined in the first flat deck aircraft carrier HMS Argus.
The American and Japanese treaty cruisers generally carried 3-4 float planes (as many as a small Great War seaplane carrier) and the catapults meant that they could be launched without slowing down (although the ships still needed to stop to recover their aircraft). The aircraft themselves were also far more capable, with top speeds of well over 100 knots and greater endurance. One of these planes could cover around 8,000 square miles of ocean in a sortie, more than doubling the cruiser's own 6,000 square mile coverage.
The performance of carrier aircraft in this period was roughly the same as that of cruiser floatplanes (indeed, in the US Navy they were actually the same machine - the Vought O2U Corsair). But while the much larger airwing of the carrier allowed for greater coverage, carriers were few in number and were extremely vulnerable when their aircraft could not operate, which meant that cruisers still played an important role.
Although there was some experimentation with large flying boats for patrol, their performance was still less than satisfactory with speeds well under 100 knots. This meant that even the largest could patrol only around 10,000 square miles - much of which would be taken up be the need to transit to the patrol area.
With a late war radar set a cruiser could cover around 14,000 square miles in 24 hours and its modern floatplanes added another 10,000 square miles each. While the European navies tended to view floatplanes as a secondary capability and continued to directly use their cruisers as scouts, the Americans and Japanese came to regard aircraft as a cruiser's primary means of scouting. This mindset was best demonstrated by the Japanese Tone-class that sacrificed their rear guns for extensive aviation facilities, including up to eight aircraft. These cruisers were designed to provide scout aircraft for carrier groups, allowing the carriers themselves to focus on operating torpedo and dive bombers.
The American navy went a different route, giving every carrier a full squadron of 18 scout bombers on top of their standard fighter, torpedo, and dive bomber squadrons. The ultimate scout bomber, the SB2C Helldiver, had a 150 knot cruise speed and a roughly 500 mile scout radius. Just as importantly, it could be outfitted to carry a surface search radar with a range of 25 miles (the much smaller cruiser floatplanes could not). In this configuration a Helldiver could scout an impressive 25,000 square miles even at night.
However, aircraft improvements were not limited to shipborne planes. The increases in speed and range meant that land based aircraft now became a potent scouting force. Patrol bombers and flying boats had patrol radii approaching 1000 miles and, by the end of the war, carried radars of their own. Thus, one of these planes could cover around 40,000 square miles in a single sortie - as much as a cruiser and its aircraft combined.
Since then, large maritime patrol aircraft have become the primary scouts for the fleet. The 150-knot Neptune was replaced by the 330-knot P-3 Orion in the 1960's and today the Orion is in the process of being replaced by the 440-knot P-8 Poseidon. Equipped with the AN/APS-154 "Advanced Airborne Sensor" and with a patrol radius of around 2,000 miles, the Poseidon can likely cover roughly 1 million square miles over the course of a sortie. Complementing this capability, the US Navy is in the process of deploying the RQ-4 Triton UAV which will be able to remain airborne for over 24 hours at a time.
The number after the slash is a rough figure showing effectiveness in bad weather.
1890's Cruiser: 4,000 / 2,000 square miles
WWI Cruiser: 6,000 / 3,000 square miles
WWI Seaplane Tender (6 planes): 9,000 / 0 square miles
WWI Carrier (12 planes): 18,000 / 0 square miles
Treaty Cruiser (4 planes): 22,000 / 3,000 square miles
Treaty Carrier (18 planes): 72,000 / 0 square miles
Treaty Patrol Plane: 5,000 / 0 square miles
WWII Cruiser (4 planes - early): 34,000 / 10,000 square miles
WWII US Carrier (18 planes - late): 225,000 / 150,000 square miles
WWII Patrol Plane: 20,000 / 12,000 square miles
Early Cold War Patrol Plane: 300,000 / 150,000 square miles
Late Cold War Patrol Plane: 400,000 / 300,000 square miles
Modern Patrol Plane: 500,000 / 400,000 square miles
(to put these numbers into perspective: the English Channel is around 22,000 square miles, the Mediterranean is 730,000, and the Coral Sea 1,400,000)
Although these figures can only be considered rough approximations at best (especially since each one is representing a number of different systems), they do give us an idea of the relative effectiveness of the various scouting platforms. During WWI, carriers were simply not an effective replacement for cruiser. While were more effective in good weather, they were useless in bad weather and had minimal combat capability.
During the treaty era, the addition of sizable air groups to cruisers kept them competitive with carriers in the scouting role. While a cruiser was inferior in a one to one comparison, this was balanced by the cruiser being significantly cheaper (and not subject to the same treaty limits) as well as capable of operating independently and in all weather.
The massive increase in aircraft performance in the 1940's destroyed this equation and made the carrier the unquestionably superior scout. The introduction of airborne radars towards the end of the war also ended the cruiser's scouting role at night and in inclement weather. At this point the debate shifted to the relative value of carrier based and land based aircraft. During the war, carrier planes remained the superior choice, but during the Cold War better radar and airframes ended this debate and the era of ships as scouts was finally over.
Here it should be noted that while helicopters are increasingly a staple of modern surface combatants, they are slower, have less endurance, and are carried in smaller numbers than the cruiser floatplanes of WWII. Thus, they should be more properly viewed as off-board sensor/weapon platforms than as actual scouts.
Early Steam
Fleet operations in late 19th century differed little from those of the Napoleonic wars. There were no aircraft or radios and even electric lighting was still a novel technology. The most advanced sensor system was a lookout with binoculars and communications were limited to signal flags, lights, and semaphore. In that time, scouting was performed by a screen of 2nd class cruisers operating ahead of the battleline, much like the frigates of Nelson's day. |
| The protected cruiser HMS Retribution |
These ships were generally capable of around 20 knots, but their triple expansion engines were unreliable at high speeds and they usually steamed much more slowly. While their lookouts could theoretically see ships out to 15 miles or so and smoke could occasionally be spotted as away as 40 miles, bad weather would reduce this considerably and spotting ships at night was all but impossible (the saying "ships that pass in the night" exists for a reason). Thus, in a 24 hour period a single cruiser could only reliably scout around 4,000 square miles and that figure could easily be cut in half by fog or rain. Further, if something was spotted, a cruiser could only communicate that fact to friendly ships that were within visual range of her signals. This meant that distant scouts were of limited use to the fleet and scouting was more tactical than strategic.
The Great War
By 1914 there had been several major advances in scouting. The first was the development of dedicated scout cruisers, typified by the British Arethusa-class. These vessels were capable of approaching 30 knots and were powered by the much more reliable steam turbines. The higher speed brought by this change in propulsion allowed these ships to cover over 6,000 square miles in 24 hours. But speed was not the only improvement as it was accompanied by powerful searchlights for identifying targets at night and wireless telegraphy for communicating over long distances. Wireless also brought with it the ability for shore installations and merchant vessels to call for help and the possibility for radio intercepts to reveal the rough location of enemy forces - both factors that played a significant role in hunting down German commerce raiders during the war. |
| The Arethusa-class scout cruiser HMS Galatea - note the prominent signal flags as well as the two searchlights on the platform abaft the funnels |
However, a new technology was also appearing - aircraft. While aircraft had revolutionized scouting for ground forces during the war, their impact at sea was much smaller. The low speed and short range of period aircraft (less than 100 knots and usually 2-3 hours respectively) meant that shore based aircraft were of little use to a fleet at sea. However, ship-based aircraft were limited to floatplanes that required their tenders to come to a stop to lower the planes into the water so they could take off or hoist the planes aboard after they had landed.
 |
| The floatplane carrier HMS Engadine, participant in the Battle of Jutland - note the large hanger for her 4 aircraft |
Despite all of these limitations, aircraft were faster than ships and could see farther. Thus, a single plane could scout around 3,000 square miles during a sortie and it was clear that they would soon become an important asset in naval warfare. The Royal Navy was at the forefront of the revolution, commissioning a dozen seaplane tenders armed with 4-8 floatplanes apiece. Later ships were equipped with a "flying-off deck" forward so that they could launch aircraft on the move. This was then supplemented with a "landing deck" aft, until finally, in the last year of the war, the two were combined in the first flat deck aircraft carrier HMS Argus.
The Treaty Period
After the war the Washington Treaty dictated ship design for the next two decades. Although navies had previously preferred smaller cruisers for scouting, the treaty drove the creation of 10,000 ton cruisers such as the American Northampton-class. At a touch over 30 knots these were somewhat faster than the older scout cruisers and their large size gave them better endurance and seakeeping as well as a much more powerful armament, but in terms of scouting ability they were essentially the same. The greatest difference was the inclusion of a hangar and catapult launched aircraft. |
| The treaty cruiser USS Northampton - note the four floatplanes on the catapults amidships as well as the prominent aircraft handling crane, the large superstructure directly beneath them is the hangar |
The American and Japanese treaty cruisers generally carried 3-4 float planes (as many as a small Great War seaplane carrier) and the catapults meant that they could be launched without slowing down (although the ships still needed to stop to recover their aircraft). The aircraft themselves were also far more capable, with top speeds of well over 100 knots and greater endurance. One of these planes could cover around 8,000 square miles of ocean in a sortie, more than doubling the cruiser's own 6,000 square mile coverage.
The performance of carrier aircraft in this period was roughly the same as that of cruiser floatplanes (indeed, in the US Navy they were actually the same machine - the Vought O2U Corsair). But while the much larger airwing of the carrier allowed for greater coverage, carriers were few in number and were extremely vulnerable when their aircraft could not operate, which meant that cruisers still played an important role.
 |
| The Vought O2U Corsair in floatplane configuration |
Although there was some experimentation with large flying boats for patrol, their performance was still less than satisfactory with speeds well under 100 knots. This meant that even the largest could patrol only around 10,000 square miles - much of which would be taken up be the need to transit to the patrol area.
World War II
The most important scouting technology introduced during the war was radar. Suddenly ships could be reliably detected in bad weather or even at night. While early radar was unreliable and short ranged, it was still an incredible improvement over visual search and by the end of the war many of the early issues had been solved. The second improvement was long range aircraft with vastly better speed and endurance. Together, these technologies transformed naval scouting into something that we would recognize today. |
| The cruiser USS Baltimore - note the extensive radar fit as well as the two aircraft cranes on the stern, the four-plane hanger is in the hull below the cranes |
With a late war radar set a cruiser could cover around 14,000 square miles in 24 hours and its modern floatplanes added another 10,000 square miles each. While the European navies tended to view floatplanes as a secondary capability and continued to directly use their cruisers as scouts, the Americans and Japanese came to regard aircraft as a cruiser's primary means of scouting. This mindset was best demonstrated by the Japanese Tone-class that sacrificed their rear guns for extensive aviation facilities, including up to eight aircraft. These cruisers were designed to provide scout aircraft for carrier groups, allowing the carriers themselves to focus on operating torpedo and dive bombers.
The American navy went a different route, giving every carrier a full squadron of 18 scout bombers on top of their standard fighter, torpedo, and dive bomber squadrons. The ultimate scout bomber, the SB2C Helldiver, had a 150 knot cruise speed and a roughly 500 mile scout radius. Just as importantly, it could be outfitted to carry a surface search radar with a range of 25 miles (the much smaller cruiser floatplanes could not). In this configuration a Helldiver could scout an impressive 25,000 square miles even at night.
 |
| The SB2C Helldiver - the white pod in the foreground is the APS-4 radar |
However, aircraft improvements were not limited to shipborne planes. The increases in speed and range meant that land based aircraft now became a potent scouting force. Patrol bombers and flying boats had patrol radii approaching 1000 miles and, by the end of the war, carried radars of their own. Thus, one of these planes could cover around 40,000 square miles in a single sortie - as much as a cruiser and its aircraft combined.
Cold War to Today
The massive improvements in aircraft and radar did not cease at the end of the war and ships continued to lose their utility as scouts. The P2V Neptune patrol airplane (introduced in the late 1940's) for example had a radius of around 1,500 miles and carried the AN/APS-20 surface search radar that could detect ships out past 200 miles. Such a combination would allow a single plane to scout an incredible 600,000 square miles - more than an entire WWII carrier task force. The carriers themselves soon had aircraft with similar sensors, if less endurance, in the form of the E-1 Tracer and later E-2 Hawkeye from the 1950's on, replacing large scout squadrons with small detachments.Since then, large maritime patrol aircraft have become the primary scouts for the fleet. The 150-knot Neptune was replaced by the 330-knot P-3 Orion in the 1960's and today the Orion is in the process of being replaced by the 440-knot P-8 Poseidon. Equipped with the AN/APS-154 "Advanced Airborne Sensor" and with a patrol radius of around 2,000 miles, the Poseidon can likely cover roughly 1 million square miles over the course of a sortie. Complementing this capability, the US Navy is in the process of deploying the RQ-4 Triton UAV which will be able to remain airborne for over 24 hours at a time.
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| The P-8 Poseidon - note how visible the ship's wake is from the air |
Scouting Comparison
Note: the following figures assume a 0.5 sortie rate for all aircraft. While this is likely pessimistic, I chose it to reflect various issues such as overlapping search patterns, the need for reserve aircraft, and wartime attrition, that are not normally accounted for in sortie rates.The number after the slash is a rough figure showing effectiveness in bad weather.
1890's Cruiser: 4,000 / 2,000 square miles
WWI Cruiser: 6,000 / 3,000 square miles
WWI Seaplane Tender (6 planes): 9,000 / 0 square miles
WWI Carrier (12 planes): 18,000 / 0 square miles
Treaty Cruiser (4 planes): 22,000 / 3,000 square miles
Treaty Carrier (18 planes): 72,000 / 0 square miles
Treaty Patrol Plane: 5,000 / 0 square miles
WWII Cruiser (4 planes - early): 34,000 / 10,000 square miles
WWII US Carrier (18 planes - late): 225,000 / 150,000 square miles
WWII Patrol Plane: 20,000 / 12,000 square miles
Early Cold War Patrol Plane: 300,000 / 150,000 square miles
Late Cold War Patrol Plane: 400,000 / 300,000 square miles
Modern Patrol Plane: 500,000 / 400,000 square miles
(to put these numbers into perspective: the English Channel is around 22,000 square miles, the Mediterranean is 730,000, and the Coral Sea 1,400,000)
Although these figures can only be considered rough approximations at best (especially since each one is representing a number of different systems), they do give us an idea of the relative effectiveness of the various scouting platforms. During WWI, carriers were simply not an effective replacement for cruiser. While were more effective in good weather, they were useless in bad weather and had minimal combat capability.
During the treaty era, the addition of sizable air groups to cruisers kept them competitive with carriers in the scouting role. While a cruiser was inferior in a one to one comparison, this was balanced by the cruiser being significantly cheaper (and not subject to the same treaty limits) as well as capable of operating independently and in all weather.
The massive increase in aircraft performance in the 1940's destroyed this equation and made the carrier the unquestionably superior scout. The introduction of airborne radars towards the end of the war also ended the cruiser's scouting role at night and in inclement weather. At this point the debate shifted to the relative value of carrier based and land based aircraft. During the war, carrier planes remained the superior choice, but during the Cold War better radar and airframes ended this debate and the era of ships as scouts was finally over.
Here it should be noted that while helicopters are increasingly a staple of modern surface combatants, they are slower, have less endurance, and are carried in smaller numbers than the cruiser floatplanes of WWII. Thus, they should be more properly viewed as off-board sensor/weapon platforms than as actual scouts.
