The ships nevertheless saw extensive service in the High Seas Fleet, Germany's primary naval formation, through the late 1900s and early 1910s, when they were used for training, which included overseas cruises.

Following the start of World War I in July 1914, the German fleet adopted a strategy of raids on the British coast, which the five Deutschland-class ships supported.

After Germany's defeat, the Treaty of Versailles permitted the postwar navy to retain several old battleships for coastal defense, including the four Deutschland-class ships.

The first tranche of vessels—the Braunschweig class—introduced the 28 cm (11 in) gun, marking a significant increase in firepower over earlier German battleships.

By the time work began on the second vessel of the 1903 fiscal year, which became SMS Deutschland, a more significantly altered design had been prepared.

Removing the turrets freed up deck space that was used to add another pair of 8.8 cm (3.5 in) guns and place the forward set of four in protective embrasures.

Deutschland and her sister ship Hannover were designed for use as flagships for the fleet and a squadron, respectively, which required additional accommodation spaces.

Tirpitz insisted on building the Deutschlands because they were the largest design that could fit in Germany's existing naval infrastructure, most significantly the Kaiser Wilhelm Canal.

Widening the canal and improving harbor facilities would be excessively expensive and Tirpitz sought to avoid another budgetary fight with the Reichstag so soon after the passage of the 1900 law.

As a result, the Deutschland-class battleships were rendered obsolescent almost immediately by the commissioning of the British HMS Dreadnought in December 1906.

[6] Because Deutschland and Hannover were completed as flagships, they had an enlarged superstructure aft to house the larger command staffs they typically carried.

Deutschland and her sisters carried several smaller vessels, including two picket boats, one admiral's barge, two launches, one pinnace, two cutters, two yawls, and two dinghies.

[6] The boats were handled with a pair of large cranes amidships; Deutschland had hers located further forward than the other members of the class.

This provided a maximum range of 4,800 nautical miles (8,900 km; 5,500 mi) at a cruising speed of 10 knots (19 km/h; 12 mph).

[12][14] For defense against torpedo boats, the ships carried a tertiary battery of twenty-two 8.8 cm SK L/35 quick-firing guns.

The guns fired 7 kg (15.4 lb) shells at a muzzle velocity of 770 m/s (2,526 ft/s), and could be elevated to 25 degrees for a maximum range of 9,090 m (9,940 yd).

All members of the class were fitted with cork cofferdams, a common practice at the time intended to prevent uncontrolled flooding in the event of shell hits.

By 1943, Hannover had been reconstructed for her planned role as a target ship, which involved removing most of her superstructure and all of her guns, though the turrets remained.

[24][25] After Deutschland entered service in 1906, she replaced the battleship Kaiser Wilhelm II as the fleet flagship, a role she held until 1913, when the new dreadnought Friedrich der Grosse took her place.

Being significantly slower than the rest of the German line of battle, the ships of II Squadron saw no action during the first stages of the engagement.

[41][42] The German experience at Jutland demonstrated that pre-dreadnoughts had no place in a fleet action with dreadnoughts, and so the Deutschlands spent the rest of 1916 on coastal defense duty in the Elbe and occasionally in the Danish straits.

In August 1917, II Battle Squadron was disbanded and most of the ships were reduced to secondary duties, being partially disarmed to free up guns for use ashore.

[19][37][43][44] Following Germany's defeat in the war, the fleet was significantly reduced in size by the Treaty of Versailles, which permitted the Germans to retain six battleships of the Braunschweig and Deutschland classes, and another two in reserve.

The two ships spent the rest of the decade training naval cadets, including a lengthy voyage to North and South America for Schlesien in 1936–1937.

During this period, Germany came under the control of Adolf Hitler and the Nazi party, which set upon a rearmament strategy and an aggressive foreign policy that led to the outbreak of World War II in September 1939.

[46][47][48] Schleswig-Holstein steamed to the Free City of Danzig in late August 1939, and was moored off the Polish military depot at Westerplatte on the morning of 1 September.

The initial German attack was repulsed, leading to heavy fighting that Schleswig-Holstein supported for the next week, and culminating in the Polish garrison's surrender on 7 September.

Later that month, Schlesien joined her sister in bombarding Polish positions along the coast, including the Hel Fortified Area.

Schleswig-Holstein was briefly reactivated in early 1942 for ice-breaker service in the Baltic, and in May she accidentally collided with a shipwreck in the Gulf of Riga, forcing a return to Gotenhafen for repairs.

[52][53] In mid-1944, Schlesien's and Schleswig-Holstein's anti-aircraft armament was considerably strengthened to allow them to be used as air defense ships in the port of Gotenhafen.