[3] The Japanese had also recognized Samarinda's importance as a center of oil and coal production, in addition to its substantial port and replenishing facilities.

[4] And with that, Samarinda became one of Japan's major seizure target in its plan to annex the Dutch East Indies.

Monteiro):[7][8] In December 1941, the General Headquarters in Bandung assigned the Samarinda Detachment the following tasks:[8] Since the Sanga Sanga drilling sites can be easily accessed from the sea through the large number of arms of the Mahakam delta, the Dutch have placed several defensive measures and detectors in the approaches to Mahakam River.

In addition, Monteiro also placed a strong guard at Dondang stream bridge in Tiram River, near where the oil pipeline was laid.

[10][11] Even though its oilfields held a special significance, the Japanese plan for the capture in Samarinda solely consisted of a mopping up operation.

[12] For this operation, the Kume Detachment will advance from Balikpapan via Mentawir to Loa Djanan (Loa Janan) up north, while the main force will advance along the Balikpapan — Sambodja (Samboja) — Samarinda road and conducted mopping up operation in Samarinda's vicinity.

forty ships, ranging from small motor boats to 100 tonnes coasters - and divided them into four groups, staffed by about 250 people under a commander.

[15] On 24 January, Hoogenband evacuated his troops from Balikpapan, rendering Monteiro to rely on civilian reports for intelligence sources.

Monteiro soon realized that the Kume Detachment will advance along a partially constructed road that runs from Balikpapan to Loa Djanan.

He ordered van Brussel, commander of the battery, to destroy the guns and fall back to Loa Djanan.

[13] On 2 February, Dutch sentries placed 12 km from Loa Djanan engaged a Japanese column that had been moving from Balikpapan to Mentawir.

Underpowered, the sentries were beaten back to Loa Djanan by the evening, after which Monteiro moved his headquarters northward to Tenggarong in order to continue delaying the Japanese advance along the Mahakam River to Samarinda II.

Along his advance, the Japanese have also attempted to entered Mahakam river via sea but failed, with two destroyers running aground in one of the delta arms.

The ship, raked with machine gun fire, had caused substantial casualties on the Japanese force for the cost of two injured crews.

Once again, AHK rejected the plan since he does not even have enough troops to delayed a still-possible enemy advance, which occurred on 8 February, as Japanese forces began marching towards Tenggarong.

Monteiro immediately urged him to relay the delaying action's futility and the need to attack Samarinda to AHK, due to several factors:[19] Still, van Beest Holle remained adamant about continuing the fight along the river to ensure Samarinda II's safety.

On 1 March, however, AHK consented to Monteiro's plan, if he agreed to continue to river action in case of failure.

The fighting continued for three hours until 10:00, when the weight of Japanese machine guns and mortars forced the brigade to retreat in panic and disorder to Kota Bangoen.

Two hours later, several Dutch soldiers arrived in a battered speedboat and informed Monteiro that the combat vessels at Kota Bangoen had engaged with Japanese armored sloops.

With Triton badly shot up and the OBM tug could no longer be used from the fight, Mahakam, along with disorganized KNIL troops in wooden boats are all that remained of the river force.

[20] Monteiro decided to organized the last resistance in Samarinda II and went there immediately to inform van Beest Holle of his disposition.

[17] Lt. Van Hossel evaded capture until 11 March, when Japanese troops caught up with him at Moeara Moentai.