Two of Norway's six Ula class submarines at their very charming looking Haakonsvern Naval Base, Bergen, Norway. These subs are only 26 years old - maybe good condition! These may possibly be sold to Poland. (Photo courtesy Petr Šmerkl, Wikipedia).
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In June 2016 Germany and Poland signed an MoU to establish a joint submarine operating command to be based in Glucksburg, Germany. This command probably is, or may become, subordinate to NATO's "Allied Maritime Command".
The authority may increase the chances that Poland will purchase German TKMS submarines - maybe new build Type 212As, Type 210mods or used Ula class subs. These would replace Poland's 5 German built ex-Norwegian Kobben class (transferred to Poland in 2002/3). In terms of used submarine sales the (average) 51 year old Kobbens may be too old to find second-hand market buyers.
Poland has again been talking to Norway about a joint submarine procurement strategy. Noting Norway's 5 existing German built Ula class subs average only 26 years old, Poland may conceivably buy them. Used Ulas from Norway would be far less expensive than new build 212As.
The small 1,000 tonne Ulas may also be quite adequate for the shorter range, mainly Baltic operations, that Poland likely undertakes. Poland has expressed interest in arming its next class of submarines with cruise missiles and they could be fired from 533mm horizontal torpedo tubes in new or used submarines.
Norway, operating in the North Sea and Arctic Ocean, may well choose Type 212As to replace its 6 Ulas.
All these submarine purchasing possibilities may also favour France's DCNS, which is also on Norway's submarine buying shortlist. France, like Germany, is a NATO country. Apparently, Sweden's Saab Kockums is not in the running as (for submarines at least) Poland and Norway, seem to favour NATO countries, something Sweden isn't.
Pete