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Few experiences compare to that of bringing a submarine to  periscope depth.  It is one of the unique evolutions which separate submarine operations from that of surface craft.

Even though periscope operations are performed with great regularity, they are, by far, one of the most dangerous routines conducted on a submarine. Yet, bringing a submarine to peri-scope depth is certainly one of the most rewarding and memorable experiences a submariner will carry with him over the rest of his life.

Having to share the oceans and seas with a great many surface craft makes coming to periscope depth a period of anxiety for all members of the submarine crew. The ship is transitioning from a relatively stable environment to one of many unknowns. During the transit, and while at periscope depth, the submarine is being placed in a very vulnerable position. The submarine bull is now close enough to the surface to be struck by most ocean going vessels. Sea pressure has been dramatically decreased, changing the stresses on all internal seawater systems and piping. The outside water temperature has likewise changed which also affects internal seawater systems. Crew members are kept busy monitor-ing and adjusting equipment to ensure vacuums are maintained, discharge rates are kept up and the integrity of seawater systems are preserved. Going to periscope depth also means valves and dampers are being manipulated to line up systems for use while at periscope depth. A valve in the wrong position could result in seawater entering what is affectionately known as the people tank.

The lives of every man onboard a submarine depends on the sound judgement of the Officer of the Deck (OOD). Unless surfaced, the submarine is always the burdened vessel and rightly must give way to all other vessels. This requires the utmost vigilance of the OOD. It also means be must be able to react quickly. While a surface ship has many eyes to scan the horizon for other vessels, there is but one eye on the periscope. An eye that is hampered by having a very limited horizon in which to search for approaching vessels due to the small distance the periscope extends above the water’s surface. Even maneuvering at periscope depth is greatly restricted due to structural limitations of the extended periscope. Additionally, rapid changes in ship speed or abrupt control surface movements raises concerns over the possibility of cavitating which would send a telltale message of the submarine’s presence.

A surface craft has a decisive advantage over a submarine which is proceeding to periscope depth in that a surface vessel can scan the surrounding waters for visual, acoustic and radio frequency emissions that reveal the presence of other craft. Until the submarine reaches periscope depth, the OOD can only count on acoustic energy to warn of nearby vessels; the presence of which may be hidden from the ship’s sensors due to the physical characteristics (temperature, pressure, salinity, presence of biologics) of the surrounding waters and the bottom conditions (hard, sand, smooth, rough, etc.) which can bend the sound energy away from the submarine. It is certainly disconcerting, but not uncommon, to have sonar report contacts where none existed before as the ship rises towards the surface.

Coming to periscope depth is always a dangerous and stressful time, but even more so when it is done at night. Ironically, the night watches onboard a submarine are sometimes relegated to the most junior qualified OOD; clearly a testament to the excellent training our submarine officers receive and the confidence their Commanding Officers have in their abilities. While a submarine operates twenty-four hours a day, the operational tempo is typically relaxed during the evening hours with fewer crew members up and about. The late night watch OOD has no one to turn to for advice. His watchstanders have never personally taken a submarine to periscope depth. He must rely solely on his own skills and judgement. His only solace is that before anyone brings a submarine to periscope depth, they must first receive the Captain’s permission to do so, providing an opportunity to express any concerns with the one most experienced to answer them. Yet, many an interesting story can be told of the late night difficulties in arousing the Captain to obtain his permission. Even more interesting stories can be told regarding the ensuing conversations .

Certainly nothing can be more frightening for an inexperienced OOD than to go to periscope depth on an overcast night. On such nights, even after the Diving Officer, who is responsible for depth control, bas brought the ship to the proper depth, one cannot be sure the scope is even out of the water. The eye can simpIy find nothing on which to focus. The OOD’s first instinct is to question the Diving Officer’s abilities. He frequently calls out to him to “Mark your depth” ; to which the Diving Officer replies with the appropriate numbers. There is this urge to raise the scope just a little higher just in case the depth gauge is inaccurate. Unfortu-nately, even if the ship is brought up a foot or two, there will still be no discernible difference in what is viewed through the periscope. The yearning for something to focus on only intensi-fies. The OOD begins to question his own eyesight, wondering if maybe his one eye was not properly adjusted for night vision. A switch is made to the other eye on the scope and again nothing is seen but pitch blackness. At this point, a decision is made to rig the control room for black in hopes that making the surround-ings darker might improve one’s chances of being able to catch a glimpse of something on the surface. Still there are few times when even this helps. The darkness of the control room only heightens the loneliness the OOD feels. If the ship is equipped with a low level light intensifier on the periscope, it is switched on as a last resort, hoping the sophisticated electronics can pick something out of the blackness. The typical result is a quivering, eerie green image that reveals nothing, but which has ultimately destroyed the GOD’ s night vision. Tensions are magnified when onboard sensors indicate that there is something out there on the surface nearby, yet the OOD reports no contacts in sight.

The clear nights can prove just as alarming. On many an approach to the surface, looking though the scope for any dark shapes or shadows overhead, the OOD is startled by bursts of light caused by the phosphorescence in the water. Other times, as he nears the surface, he may see some flickering light shining back down through the sea at him that he realizes is not caused by the phosphorescence in the water. His first instinct is that it may be the light of a ship overhead. Before he can even react, the scope is clear of the water and he finds himself staring at a huge bright object. Many an inexperienced OOD has quickly returned the submarine to the safety of the depths only to learn that the bright object he so feared was nothing more than the moon. Even the stars can be a hindrance for a submariner on a dark night. As the OOD conducts his periscope scan, he finds himself wondering as to whether he is staring at stars or the running lights of some vessel on the horizon.

Being on the scope at night gives one an appreciation of how lonely it is to be at sea on a submarine. Each second seems like hours. The eyes begin to play tricks on you as you begin to see lights and objects that do not exist. The OOD is anxious to get all the chores that must be done at periscope depth over with as soon as possible. It is at these times that the true difference between the surface sailor and submariner come to light, for while the surface sailor only feels secure in the safety of a harbor, the submarine sailor longs for the safety of the depths.

With time each OOD will come to appreciate and long for the presence of a full moon and cloudless night. For even at night the sea has a special beauty about it. For those truly fortunate, they might get to witness the awesome fury and magnificent light show of a thunderstorm at sea. As the submarine slips back into the murky depths, each 000 can feel content knowing that they have done something few other people will ever experience in their lives.

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