Perhaps because the 1500-ton displacement was close to that of a large destroyer, the construction period of the U139 submarine was much longer than that of the typical U and UB type submarines. It wasn't until April 1918 that the submarine assigned to Zhang Hainuo's crew, named U148, completed its final assembly.
Unlike the rushed departure for combat after taking over U171, this time the Navy gave Zhang Hainuo two weeks to lead his crew in familiarizing themselves with and inspecting the submarine. Although the newly commissioned submarine did not suffer from the aging of parts like older submarines, it still required a thorough inspection of its watertightness, engines, and other major components, much like a newly built ship. The craftsmanship of the German shipyards had been well proven in the Battle of Jutland, and apart from some lines needing fixing and adjustments, U148 performed well in full-speed sailing and maximum diving tests. Its maximum surface speed reached 17.2 knots, while underwater, it could achieve 8.8 knots, maintaining normal operations even at a depth of 50 meters.
Until the day before U148 received its departure orders, Zhang Hainuo would smile knowingly at mealtime, proud to command what he considered to be the foremost ocean-going submarine. This sentiment was shared to some extent by the other crew members, especially the seasoned ones. The submarine had 32 bunks, accommodating two-thirds of the crew, with provisions sufficient for all crew members to live at sea for 10 to 12 weeks. There was even a small refrigeration room onboard. Though still far from the comfort of large warships, these conditions were a vast improvement compared to other submarines, especially the old U7.
On May 4, 1918, Zhang Hainuo received his first operational command as captain of U148. The order required him to command the ocean-going submarine to cross the Atlantic and operate in the eastern waters of the United States. The mission was to sink valuable American ships and blockade American ports using submarine-launched mines.
(This sounded much like the tasks of German ocean-going submarines in the later stages of World War II, but based on Tiankong's research, the German Navy during World War I did have such capabilities and had executed such missions.)
The order also required Zhang Hainuo not to disclose the contents of the instructions to anyone, including his crew, before departure. Furthermore, throughout the operation, he was to maintain radio silence as much as possible to avoid revealing his whereabouts. Once U148 set sail, as the captain, Zhang Hainuo enjoyed a high degree of authority over the submarine, even having the final say on which American port to target.
Having previously speculated on this matter, Zhang Hainuo was not particularly surprised by the content of the command. However, the American topographic map issued by the Navy along with the order disappointed him greatly. This map, with a scale of 1:20,000,000, was barely suitable for travel, let alone executing combat missions. The inadequate preparation of the German Navy for this operation could be inferred from this fact (a common phenomenon during World War I)!
Recalling the Maltese sea chart used by Hessen before, Zhang Hainuo told himself that if he ever came to power, he would ensure detailed sea charts of the four continents and five oceans were prepared before the outbreak of war, preferably including underwater topographic maps. Because searching for them when needed would be too late!
Designed from the outset as a "cruising submarine" capable of transoceanic operations, the U139 submarine had a row of vertical containers below the aft deck for storing mines, capable of carrying 12 floating mines for underwater deployment.
This may sound like something from World War II submarines, but German submarines had already possessed this technology during World War I. Another class of similar specifications, the UE-type cruiser mine-laying submarines, could even carry 32 mines and operate along the eastern coast of the United States. Thinking back on the nearly 20 years from 1918 to 1935 when Germany did not build submarines, yet its submarine technology still outstripped that of other countries during World War II, one could see the German talent for submarine weapons!
With the fuel and ammunition already loaded aboard, and the final batch of fresh vegetables and meat brought on board, Zhang Hainuo took a last look at the familiar harbor before confidently commanding U148 to set sail.
After the submarine left Wilhelmshaven, Zhang Hainuo immediately convened all crew members to announce the radio silence command and informed them that U148 would be heading to the eastern waters of the United States for operations.
Upon hearing this news, almost every crew member showed surprise and excitement. From Germany to the United States, even taking the shortest route would cover over 4000 nautical miles. No one on board, including Zhang Hainuo, had ever been to such a distant place as a crew member. Aside from the potential dangers and unpredictable sea conditions along the way, even sailing continuously at the submarine's surface cruising speed would take 18 to 20 days!
In other words, it would be a long and arduous journey!
(PS: During World War II, some German submarines took more than a month to sail to the United States. This was mainly because British and American anti-submarine reconnaissance capabilities were strong, and German submarines often had to use snorkels to travel underwater during the day, resulting in significantly slower speeds compared to surface sailing.)
With the British becoming increasingly vigilant, suitable targets were becoming scarce in the North Sea, English Channel, and eastern Atlantic waters. Sailing to North America was akin to embarking on a Spanish-style adventure and gold rush in the eyes of the German Navy. The Americans were known for their wealth and generosity. As long as they sank a few American ships or liners, honors, rewards, and promotions were within reach.
Zhang Hainuo was well aware of the pros and cons of this endeavor. He immediately made the first mobilization speech to the crew after departure:
"Boys, the attacks on the ports of North America have just begun. It's like the North Sea and the Scottish Sea of 1914; American ships are everywhere, poorly guarded. We are like wolves; once we cross this ocean, we can enter the sheep
fold. There are no hunting dogs, no traps, just opportunities. That's the wolf's paradise! When we return, I promise that each of us will wear a medal on our chests!"
"At the same time, I hope everyone pays attention to three points before reaching North America: First, no one should be lax on duty. Once something goes wrong, there will be no one to rescue us in the vast ocean away from home! Second, although our freshwater theoretically lasts for two and a half months for all, I ask everyone to save water as much as possible to ensure we have enough freshwater for any sudden situation. Third, communicate more with your comrades to avoid depression and low spirits due to the long sea voyage. If you notice any abnormal behavior from your comrades, report it to me immediately. Remember, this report is not to punish anyone but to help us all!"
"Do you understand?" Zhang Hainuo asked loudly at the end.
"Understood!" the crew responded enthusiastically.
Zhang Hainuo nodded in satisfaction. The journey had just begun, and he needed to constantly motivate these crew members, especially the newcomers, whose experience and psychological resilience were not as strong as the seasoned sailors. This long voyage was their best opportunity for growth.