In peacetime and wartime the intensity of ASW surveillance makes submarine operations on the surface and even at snorting depth dangerous. In Baltic operations quiet on-battery and/or on-AIP operation may be essential. It is probably no coincidence that the two nations that have developed the most efficient and commercially successful AIP systems (Germany (with fuel cell) and Sweden (Stirling engine)) may well spend most of their operating time in the Baltic.
The approaches to sea bases and coastal cities/ports frequently have sensor protections using undersea arrays such as:
- Malsten station (old probably non-operational hydrophones/sonar and magnetic anomaly) and much more operational, modern and geographically dispersed equipment
- approaches to Helsinki Harbour (hydrophones/sonar, magnetic anomaly and more modern sensors)
- Russian Baltic Fleet Base at Kaliningrad Enclave much more extensive and intensive. Few details about Russian hydrophones escape the Russian information censors. Naturally Russians submarines have many types of ASW sensors and the Russian Northern Fleet deploys test sensors
Little seems to be known in the open-source world about Russian submarine operations in the Baltic. Russian Kilo submarines and even Russia's one or two Ladas appear unsuited due to their relatively large size and lack of (known) AIP.
Russia, of course, has relied on highly developed nuclear propulsion solution for its AIP-like needs. But the Baltic is the wrong environment for nuclear propulsion as nuclear is assumed to be noisier than AIP, tends to preference large submarine solutions far heavier than 2,000 tons (surfaced), promotes speed which is a major danger in Baltic operations and nuclear submarines are an expensive asset to be at risk from highly intensive Baltic ASW forces and dangerous natural geography of the Baltic.
- the need to keep secret the efficiency of anti-submarine sensors (including sea-floor arrays) in detecting Russian (or friendly countries)
- the much greater political, economic and military power of Russia compared to all other Baltic counties. Non-NATO Baltic countries Sweden and Finland are particularly careful not to offend the Russian giant by publically identifying clearly Russian submarine acoustic signatures and radio transmissions.
- normal diplomatic practice which keeps sensitive international issues secret
- the natural secrecy of Governments-Navies relating to all submarine operations
- for a defending Navy (like Sweden's) to be publically seen as unable to counter submarine intelligence gathering against one's country can be embarrassing all round.
- as the weaker country, compared to Russia, Sweden is forced by Russia or finds it more politically convenient, to recant and deny there was any Russian submarine incursion in the first place
Note how the detection and weaker country recanting process plays out in Russia vs Sweden October 17-24, 2014:
This October 2014 Submarine Matters article contains more detailed descriptions of recent Russian mini-submarines in the Baltic.
Tomorrow some surprisingly advanced Russian UUVs will be revealed.