C/W's Robertson & Watson.
Top Secret   Copy No. 171.                    85
    U-boat  "U-249".
    Rec:        6.12.44.
    Reg No:  Top Secret 132.
        Current Order No: 1.  Issued Nov. 1944.
        (Procedure when underway and in operational areas).
I.        The Schnorchel has to a considerable extent, escaped enemy air attack and with the simultaneous decrease in U-boat losses, has enabled them to operate again, in areas strongly defended by aircraft.
Principles for Proceeding.  The task of the Commander is to take the boat to and from the area of operations without any great diversions, to avoid skirmishes with the enemy defence, to utilize however, every opportunity for attack.
Principles for the operational zone.  In order to make full use of the possibilities offered by the Schnorkel, approach close to the enemy shipping near the coast.  Only there, are successes to be obtained.
II.        Procedure of boats when underway and when in the operational zone depends on the strength put up by the enemy air force.  Commander U-boats differentiates between areas with a strong, medium and weak defence.  If a Commander establishes another aircraft position in an area, as described under A - C, he can intensify or modify his tactics according to the change.
A. Strongly defended areas.  Squares AN, AF, AE, AM, BF, CG, DJ, AL, BE of the eastern third, further a strip of nearly 100-200 nautical miles off North and South America, including the Caribbean.
  Procedure:  on principle proceed submerged when underway and when on operations, recharge when Schnorkelling (total submerged warfare).  Recharge only above surface, only when Schnorkelling is not possible for technical reason.
1. On setting out and returning when Schnorkelling.
  a). For more detailed instruction concerning schnorkelling times, boat routine, making best of weather conditions, see Current Order No. 20.
  b). Normal cruising depth above 50 meters (162.5 feet) - At routine times and when taking hydrophone effects at periscope depth.  Good hydrophone conditions in no way exclude periscope observations while proceeding.
2. When setting out and returning while submerged with charging above surface.  Only in cases of a faulty Schnorkel or when other reasons (e.g. a too strong current) make it necessary.
  a). Charging to be carried out, in conditions unfavorable for air attack, that is, in general, by night.  Favorable - moonless, very dark, haze, fog, storm.
  b). If at night especially great air and radar activity are observed, charging can be carried out in the daytime, in fog, or in clear weather with good visibility and good Ack Ack conditions.  In case of doubt the proceeding by night is more favorable, since, in the event of an attack, better opportunity is afforded for submerging and for shaking off the contact, moreover, a simultaneous attack from several aircraft is difficult.


    C/W's Robertson & Watson.
  c). During charging, complete Ack Ack readiness.  Commander on the bridge.  Keenest lookout.  All armament ready and unmasked, so far as weather conditions allow.  Gunner in layer position with shoulder-piece in position.  In weather conditions which enable accurate surprise attacks, if necessary man only the twin barrelled gun, in order to be able to submerge more quickly when located.
  d). Set up the available FUMB.  If there is FUMO on board, warm up well before surfacing, and use as follows:-  Immediately after surfacing a circular sweep with the FUMO, then only Radar observation with "Wanze" and/or "Borkum and Tunis".  If airborne locator has been observed, in general, submerge.  If charging is urgent, when detecting a locator, D/F with FUMB, search by FUMO, and continue to observe the enemy.  Until picked up by FUMO, a longer period (up to 30 mins.) can elapse.  If no enemy is detected, do not return too soon to FUMB.  If the "Hohentwiel" set is in perfect order and the servicing crew well-experienced, the apparatus, in continuous search alone may be used, when underway as an air-raid siren.
  e). Do not remain on the surface longer than the time required for charging, as this endangers the boat unnecessarily.  Exceptions:  In especially unfavorable flying conditions and if the FUMO is functioning perfectly.
III.        Procedure in the operational zone.
A. Submerged on principle and only while schnorkelling.  On breakdown of the Schnorkel, in general, return to base.  In this case carry out charging as under 11.
B. Keep close to traffic focal points and to coast routes, for it is only there that interception of traffic can be guaranteed.  Lying on the bottom and taking advantage of the density of water which renders it more difficult for the U-boats to be intercepted by hydrophone and radar, facilitate, according to the latest experiments, a successful U-boat operation even at a depth of well under 100 metres (325 feet).
C. Initiate all measures for daylight attack, since this is most favorable.  Submerged night attack promises success only at full moon.
D. Go frequently to periscope depth, do not rely upon the hydrophone.  By night and when there is traffic, go down to the bottom, to save batteries.
IV.        General Rules for "total submerged warfare".
A. Avoid surfacing by astronomical reckoning as far as possible.  According to experiments so far to hand, extremely exact determination of position is made possible by very accurate dead reckoning, by taking the current into consideration and by making full use of the sounding device, electrosone and radio-beacons.  When close to our own, or to enemy coast, make full use of every means of determining a position by land.
B. As it is not possible to service weapons before putting out or before starting out to proceed under water cruises for any lengthy period, well lubricate the armament.  Submerged cruising damages the armament less than the continual change between air and water.  Surfacing, necessitated by other causes, should be used in servicing the armament.
C. Even when proceeding without incident under water and when on operations, it is necessary to reduce the consumption of air and current to the minimum, in order to shorten the charging time and to have sufficient battery capacity for the attack when contacting the enemy, and further, in case of pursuit, to be able to run on it long enough without being forced to Schnorkel and/or surface.
D. Especially when the Schnorkel  is out of order the boat must continue to run submerged in order to evade the shadowing aircraft and to be as far


    C/W's Robertson & Watson.
  as possible beyond the range of location of the point of submerging, when it surfaces.  Therefore when below water, not more than slow speed ahead, both engines.  Use only the most necessary consuming plant, economize on light and air, the E-condenser consumes much current.  Trimming and pumping with the auxiliary bilge pump.  Carry out night routine according to Current Order No. 2.
B.        Areas with medium air defence.
  Areas not specified under A).  Atlantic - North of 15 degrees South, coastal strips 100-200 nautical miles off the African coast, fringes of the Indian Ocean, including islands.
  Procedure:  Submerged by day, above surface by night.
  a). In the open Atlantic between 30 degrees North and 15 degrees South, in clear, cloudless weather, with good Ack Ack conditions and with the FUMO switched on, proceed on the surface; without the FUMO, on principle, submerged.  FUMB locating has been intercepted, dive and remain for a while submerged.  If the enemy holds you on his Radar beam, he later sends out carrier planes, operating from sight.
  b). Above water keep Ack Ack gun ready for firing and by day at least six look-outs on the bridge.
C.        Areas with weak air-defence.
  Atlantic - South of 15 degrees South, open spaces of the Indian Ocean.
  Procedure:  On principle, on the surface, FUMB continually switched on.



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