The Australian Navy's first successful offensive against Japan was the sinking of Imperial Japanese Naval Submarine 'I-124' on 20th January 1942 north-west of Darwin at 12 degrees 07'S; 130 degress 09'E.
The following report was submitted by LCDR D.A. Menlove RANR(S) CO of HMAS Deloraine. LCDR W. Eric Thompson RANR was the Gunnery Officer.

COMMANDING OFFICER HMAS DELORAINE - 23rd JANUARY 1942
NAVAL OFFICER IN CHARGE, NORTHERN TERRITORY
ATTEMPTED TORPEDOING OF HMAS "DELORAINE' AND COUNTER ATTACKS CARRIED OUT.
SUBMITTED FOR INFORMATION.

1. At 1155 (K.L) on Tuesday 20th January, 1942 whilst carrying out Double Oropese Sweep of searching channel off Port Darwin, a signal was received by W/T from Naval Officer in Charge, Darwin, ordering Deloraine to "Proceed forthwith to position 12 degrees 08's 130 degrees 10'E, for submarine sighted 0630 today Tuesday. Attacked by "Aldon" (US Destroyer) U.S Aircraft and Destroyers will co-operate" T.O.R 1154 (K-L)
2. Speed was reduced to 8 knots and sweeps recovered with all effort consistent with speed and safety. Immediately on recovering of sweeps at 1203 speed was increased from 8 knots in steps of two knots to 14 knots and course 275 degrees set to reach position given in your signal.
3. Speed of 14 knots was attained at 1224. I did not order a higher speed taking into consideration the fact that I might need this higher speed later for an emergency.
4. Course was altered at 1250 to investigate a floating object bearing 356 degrees, and at 1300 object was identified as a sand hill on Bathurst Island which had been partially obscured by a rain squall.
5. Course was reset at 256 degrees at 1300 to reach the signalled position and I estimated that Deloraine would be in that position at 1336.
6. At 1335.5 I moved out to starboard wing of bridge prior to giving the necessary orders to alter course to 323 degrees to close aircraft which had just been sighted. The starboard lookout Able Seaman O'Neill gave an alarm "TORPEDO APPROACHING GREEN 100", and I ordered the helm to be put hard to starboard, and full speed on the engines. The ship responded quickly and the torpedo passed 10 feet astern. When ordering full speed I also sounded off "ACTION STATIONS"
7. A bearing of the torpedoes wake was 336 -156 degrees and an aircraft was observed flying towards me on the reciprocal bearing of 156 degrees.
8. At 1338 course was steadied 336 degrees to close submarine which was then straight ahead by Asdic Contact range 2500 Yards. Echo received slight opening doppler.
9. Three planes were observed circling over position from which Asdic contact was obtained. One Catalina flying boat and two American float planes.
10. At 1343 attack was carried out with pattern of charges - Port Rail 150 feet, Port Rail 250 feet.
11. After explosion of pattern large oil and air bubble' were plainly seen, and altered to reciprocal course to make second attack.
12. At 1346 ship was steadied on reciprocal course proceeding towards centre of oil and air bubbles, Asdic Contact Steady. At 1348 fired second pattern of two charges from rails both at 250 feet, submarine surfaced at 1349 showing periscope and bow. It was clearly noticed that submarine was trimmed about 5 degrees by stern; and listing at least 20 degrees to Port. Periscope appeared black and base rusty colour.
13. Immediately I altered course to bring port thrower to bear on periscope and fired with a depth charge setting of 100 feet. This charge was observed to land no more than 100 feet from periscope, submarine at that time was endeavouring to crash dive. About 10 seconds after our depth charge landed in water an aircraft dived and dropped a bomb within feet of our depth charge. The bomb appeared to burst on contact with water, and about one second after depth charge explosion.
14. Course was altered to open Asdic Range for further attacks and at range of 1200 yards re-altered to close for attack.
15. At this juncture it was reported that submarine was steady - no doppler this indicating submarine was stationary and evidently on bottom. Oil and air bubbles continued to come to surface in very large quantities, and I am firmly of the opinion that submarine was then crippled.
16. At 1346 another attack was made with pattern of six depth charges settings staggered in similar manner to first pattern.
17. Range was opened to 2000 yards after firing this pattern and then steamed through area to make further observations. Again it was clearly seen that large Oil and air bubbles were rising to surface and Asdic Contact was good, showing no Doppler. Samples of Oil were collected in buckets as we passed through area and appeared quite definitely(sic) to be a type of engine oil. Many particles of T.N.T were observed floating in the area. At this stage there were only five depth charges remaining and it was considered wise to conserve these for a possible emergency and if necessary carry out single attacks later.
18. In giving position of this attack it is requested that consideration be given to my statement of "estimated position", as it was not possible to obtain good fixes from land on Bathurst Island owing to heavy rain squalls an distance of land marks. "Estimated position" in which attack was carried Lat12 degrees 07'S. Long 130 degrees 09'E. Furthermore tides off Port Darwin are strong and difficult to estimate effect in this area.
19. Communication by W/T at time of first attack was regrettably not possible owing to transmitter developing fault on firing first pattern of depth charges, attempts were made to pass this message to you via Catalina' flying boat but difficulty was experienced in passing message by light. Later however, flying boat did report having cleared message to you.
20. As no other ships had arrived at scene of attack I remained crossing and recrossing to retain Asdic Contact. Throughout the following half hour 1400-1430 we had perfect contacts with no Doppler - target stationary. Oil and Air observed to be rising continuously which confirmed my belief(sic) that submarine had been put out of action permanently.
21. At 1430 whilst crossing through oil patch at scene of first attack another echo was heard approximately 125 degrees 3000 yards from us.
22. Investigation of this echo was made forthwith and considered to be submarine echo. It was then decided to manoeuvre to position and carry out deliberate attack on this new Asdic Contact which had no apparent doppler.
23. At 1440 attack was made with pattern of two depth charges from rails at staggered settings of Port side 150 feet, Starboard side 250 feet. Very definate (sic) Oil and Air Bubbles were seen to rise after this attack. A further attack was carried out at 1450 over the same spot as Asdic Contact remained, charges were fired as follows Port rail 150 feet, Starboard rail l50 feet, Port rail 250 feet.
24. The depth of water in all these attacks was approximately 24 fathoms.
25. At 1500 signal was made to notify you that all my depth charges had been expended.
26. It was decided to remain and keep both contacts until other vessels arrived.
27. There was no difficulty experienced in holding the two contacts and at 1610 I sighted Lithgow approaching from Eastward, so turned to meet her in order to lead her to position.
28. At 1620 I altered course leading Lithgow to position, and at 1630 asked him for his DR position to allow me to check my own. These positions were reasonably close.
29. I notified Lithgow at 1700 that I had passed over position and immediately hauled out of line to take position and act as directing vessel for her. Katoomba approached and signalled to me at 1748, and I passed all possible information to her.
30. At 1927 Katoomba ordered me to proceed to meet Vigilant to emb9rk depth charges and return to meet him at scene of defunct submarine at daylight next day.
31. Vigilant was contacted and fast alongside me at 2210. At 2325 Vigilant cast off and I proceeded in execution of Katoomba's previous orders.
WEDNESDAY 21st. JANUARY 1942
At 0305 when approaching rendezvous a submarine echo was obtained, Action Stations sounded and at 0321 passed 1st Dan Buoy marking defunct submarine. As Asdic Contact was firm I decided to attack again, and at 0322 fired pattern of two depth charges from rails both set at 250 feet.
It was seen a few minutes later that oil patch had apparently increased and a very strong smell of oil was most noticeable.
As no vessels were sighted in area I made a further attack with pattern of two depth charges of similar settings to those at 0322.
Asdic Contact remained firm and I crossed over area until meeting Katoomba at 0356.
In accordance with Katoomba's orders I commenced search southward of position and joined her at daylight.
From daylight until 1155 I acted under Katoomba's order; and during that time fired my remaining eleven depth charges in combined attacks with her.
At 1155 I proceeded toward harbour and secured to G1 Buoy at 1708.
I have much pleasure in reporting that throughout the above mentioned Actions my Officers, and Ship's Company carried. out their various duties in a most willing and capable manner.
I have the honour to be, Sir
Your Obedient Servant
Signed O.A. Menlove
Lieut Commander RANR(S)
Commanding Officer